The race for U.S. Senate in Montana between Democratic incumbent Jon Tester and Republican Matt Rosendale is too close to call.
As of 3:45 a.m. EST on Wednesday, Rosendale holds a lead of 6,082 votes out of more than 355,000 cast - a margin of roughly 1.7 percent.
Roughly a third of precincts remain to be counted.
The race for U.S. Senate in Arizona between Republican Martha McSally and Democrat Kyrsten Sinema is too close to call.
As of 3:45 a.m. EST on Wednesday, McSally holds a lead of 17,240 votes out of more than 1.6 million cast - a margin of roughly 1 percent.
Roughly 25 percent of votes in Arizona are counted after Election Day.
The race for U.S. Senate in Florida between Democratic incumbent Sen. Bill Nelson and Republican Rick Scott is too close to call.
With all precincts reporting as of 3:45 a.m. EST on Wednesday, Scott holds a lead of 38,717 votes out of more than 8 million cast - a margin of less than one half of 1 percent.
Under state law in Florida, a recount is mandatory if the winning candidate's margin is less than 0.5 percentage points.
The Associated Press does not call any race that may proceed to a recount.
Democrat Jacky Rosen has defeated incumbent Republican Dean Heller in a hard-fought battle for a U.S. Senate seat in Nevada, giving Democrats a key pickup in the chamber.
Rosen on Tuesday ousted Heller, who has been in office since he was appointed to fill a vacancy in 2011.
Heller was considered the most vulnerable Republican running for re-election to the U.S. Senate this year as the only one seeking another term in a state that Hillary Clinton won in 2016. He conceded earlier in the night.
Heller was once a critic of President Donald Trump, but the two have become allies. Rosen painted Heller as a rubber stamp for the president and counted on backlash to Trump to help her oust the incumbent.
Rosen's win puts Nevada with half a dozen other states represented by U.S. senators who are both female. Nevada's other senator is Democrat Catherine Cortez Masto.
U.S. Sen. Dianne Feinstein has won a fifth full term representing California after shaking off a challenge from a fellow Democrat who argued she hasn't been tough in confronting President Donald Trump.
Feinstein defeated state Sen. Kevin de Leon.
Voters first sent Feinstein to Washington in 1992. At 85, she is the oldest current U.S. senator.
She faced a fellow Democrat because of California's system that sends the two candidates who win the most primary votes to the general election.
The race failed to generate much excitement, with Democrats more focused on winning seats in the U.S. House than on a safe Senate seat.
Feinstein argued that her experience and tenure in Washington made her the best person to serve California.
Maine's independent Sen. Angus King has withstood a challenge from opponents on his ideological right and left to retain his seat.
King, a popular former Maine governor, defeated Republican state Sen. Eric Brakey and Democratic activists Zak Ringelstein to win a second term on Tuesday. King caucuses with the Democrats and was first elected to the Senate in 2012.
Tuesday's election was the first U.S. Senate race to use Maine's ranked-choice style of voting.
Brakey or Ringelstein could have forced additional voting rounds under the system if King had fallen short of 50 percent of the popular vote. But King, who has long been popular with Maine voters, had a decisive win.
Republican Josh Hawley has unseated Missouri's Democratic Sen. Claire McCaskill in a national victory for the GOP.
Republicans have long hoped to flip McCaskill's seat in the increasingly Republican state. Missouri was once considered a bellwether known for picking the successful presidential candidate, but it's since lost that status and trended right.
President Donald Trump won the state by nearly 19 percentage points. Missouri's attorney general pinned his campaign to his support for the president.
McCaskill was one of 10 Democratic Senate incumbents up for re-election in states Trump won.
Voters first elected McCaskill to the Senate in 2006. She won re-election in 2012 after Republican candidate Todd Akin said women's bodies can prevent pregnancy in cases of "legitimate rape."
Democratic Sen. Maria Cantwell has won re-election in Washington, beating Republican challenger Susan Hutchison.
Cantwell easily outdistanced Hutchison, a former Seattle TV anchor and state GOP chairwoman.
Cantwell is a former tech executive who previously served one term in the U.S. House and six years as a state representative in the state Legislature. She will be serving her fourth term.
It's been nearly a quarter century since the GOP has captured a major statewide race in Washington.
The last time voters sent a Republican to the U.S. Senate was 1994, when Sen. Slade Gorton was re-elected to his final term before being ousted by Cantwell in 2000.
Democrat Debbie Stabenow of Michigan has won a fourth term in the Senate, defeating Republican challenger John James.
Stabenow campaigned as a pragmatic lawmaker who forges bipartisan agreement despite the partisan rancor in Washington. She cited her work shaping farm legislation and pushing a new law that allows pharmacists to tell consumers when they can save on prescriptions by paying cash instead of using insurance.
The 68-year-old Stabenow criticized President Trump's attempt to slash federal funding for the Great Lakes. She said James would have been an unabashed enthusiast of Trump with no governing experience.
James is a black combat veteran and business executive. Trump won Michigan in 2016. He called James "a star" candidate.
Mississippi's U.S. Senate special election is headed to a runoff, and the state's voters will either elect a woman to the office for the first time ever or a black man for the first time since Reconstruction.
Republican Cindy Hyde-Smith and Democrat Mike Espy advanced Tuesday from a field of four. They compete in a Nov. 27 runoff, and the winner will serve the final two years of a term started by Republican Sen. Thad Cochran, who retired in April.
Republican Gov. Phil Bryant appointed Hyde-Smith, who was state agriculture commissioner, to temporarily succeed Cochran until the special election is decided. She is the first woman to represent Mississippi in Congress, but no woman has been elected to the job from the state. She is endorsed by President Donald Trump.
Espy is a former congressman and former U.S. agriculture secretary.
Democratic Sen. Mazie Hirono of Hawaii has defeated Republican Ron Curtis to win a second term.
Hirono had an advantage going into Tuesday's midterm election as an incumbent with broad name recognition. Her challenger is a retired engineer who had never run for public office.
Hirono has served in the legislature, as lieutenant governor and as U.S. representative. The 71-year-old kept a relatively low profile early on in the Senate, but has gained attention for her outspoken opposition to President Donald Trump and his policies.
Hirono urged men to "shut up and step up" when the Senate was considering confirming Justice Brett Kavanaugh's nomination to the U.S. Supreme Court.
Some Hawaii voters cheered the statement, while others accused her of being anti-male.
Democratic Sen. Tina Smith has won Minnesota's special election to finish the final two years of former Sen. Al Franken's term.
Smith defeated Republican state Sen. Karin Housley on Tuesday. The election was a 10-month sprint, triggered in January after Franken resigned amid a growing sexual misconduct scandal.
Smith got a head start in the race when she was appointed to take the seat by Democratic Gov. Mark Dayton. Smith was Dayton's lieutenant governor and former top aide.
Housley tried to brand Smith as a political insider. But national Republican groups largely bypassed Housley's race, sinking resources instead into more winnable races in states like North Dakota and Indiana.
Republican Sen. Deb Fischer has cruised to a second term in Nebraska, defeating Lincoln city councilwoman Jane Raybould.
Fischer won Tuesday despite Raybould's efforts to cast the first-term incumbent as a Washington insider who sided with her party even when it was harmful to the GOP-friendly state. Raybould pitched herself to voters as an outsider who would look for ways to lower health care costs.
Fischer rejected the criticism and noted her work on Senate committees focused on agriculture and the military, both important areas to Nebraska with its farm economy and Offutt Air Force Base.
The candidates differed on their support for new U.S. Supreme Court Justice Brett Kavanaugh, who faced sexual assault allegations during his confirmation process. Kavanaugh denied the allegations. Fischer voted to confirm Kavanaugh, while Raybould said the allegations merited further investigation.
Republican Marsha Blackburn has won a grueling, expensive contest to become the first female U.S. senator from Tennessee.
The congresswoman defeated Democratic former Gov. Phil Bredesen on Tuesday by closely aligning her bid with President Donald Trump. The president made three visits to the state for her.
Blackburn has sought to undermine Bredesen's reputation as an independent thinker by tying him to national Democrats at every turn. Blackburn was first elected to the House in 2002 and has called herself a "hardcore, card-carrying Tennessee conservative."
Blackburn will replace retiring Republican Sen. Bob Corker. She represents a rightward shift from Corker and other more centrist senators that Tennessee has historically elected.
Republicans have retained Senate control for two more years, shattering Democrats' dreams of an anti-Trump wave sweeping them into majority.
The result was all but assured when Republican Kevin Cramer ousted North Dakota Democratic Sen. Heidi Heitkamp and when Republican businessman Mike Braun ousted Sen. Joe Donnelly in Indiana.
Meanwhile, Sen. Ted Cruz fended off a spirited challenge from Democratic Rep. Beto O'Rourke, and Republican Sen. Marsha Blackburn triumphed in Tennessee.
The GOP's gains come even as the results in Nevada and Arizona have yet to be determined.
Former Republican presidential candidate Mitt Romney has handily won a U.S. Senate seat in his adopted home state of Utah after a campaign where he backed off his once-fierce criticism of Donald Trump.
Romney clinched the win Tuesday as he defeated Democrat Jenny Wilson, a member of the Salt Lake County council.
Romney was the heavy favorite to win the seat in conservative Utah, where he holds near-celebrity status as the first Mormon presidential nominee from a major party.
He replaces longtime Republican Sen. Orrin Hatch, who chose not to seek re-election.
Romney denounced Trump as a "fraud" and a "phony" during the 2016 campaign, but has since said he approves of many Trump policies.
Republican Sen. Ted Cruz fended off rising-star Democrat Beto O'Rourke to win re-election in a much-watched Texas race that began as a cakewalk but needed a visit from President Donald Trump to help push the incumbent over the top.
Cruz finished a surprising second in the 2016 Republican presidential primary and began the Senate race as a prohibitive favorite.
But O'Rourke visited fiercely conservative parts of the state that his party had long since given up on, while shattering fundraising records despite shunning donations from outside political groups and pollster advice.
Cruz argued that his opponent's support for gun control and universal health care were too liberal for Texas.
Trump and Cruz were bitter 2016 rivals, but the president visited Houston late last month to solidify the senator's win.
Democratic Sen. Joe Manchin of West Virginia has turned back a challenge by Republican Patrick Morrisey to win his second full-term in a state carried by President Donald Trump.
Manchin survived the most difficult re-election campaign of his career against the comparative newcomer Morrisey. Manchin is a former governor who has held elected office in West Virginia for the better part of three decades.
Manchin heavily outspent Morrisey and portrayed himself as loyal to his home state rather than party ideology. Manchin was the only Senate Democrat to vote to confirm Supreme Court nominee Brett Kavanaugh.
Manchin was critical of Morrisey's New Jersey roots and his past lobbying ties to the pharmaceutical industry.
Morrisey is a two-term state attorney general and a staunch Trump supporter.
Democratic Sen. Tammy Baldwin of Wisconsin has won a second term, fending off a challenge from a Republican who ran as a staunch supporter of President Donald Trump.
Baldwin led Leah Vukmir in fundraising and polls throughout the race.
Baldwin is one of the most liberal members of Congress. The differences between her and Vukmir were stark. They disagreed on almost every issue.
Baldwin made the campaign largely about health care and Vukmir's opposition to the Affordable Care Act. Baldwin argued for keeping the law and its guarantee of insurance coverage for people with pre-existing conditions.
The race was Wisconsin's first for Senate where both major party candidates were women.
Democratic Sen. Amy Klobuchar has easily won a third term in Minnesota.
Klobuchar defeated Republican state Rep. Jim Newberger on Tuesday. It comes as Klobuchar's name swirls amid the crop of potential Democratic presidential candidates for 2020.
The race was never close. Newberger is a little-known state lawmaker who struggled to raise money against the popular Klobuchar.
Republicans put far more focus on the state's other Senate race to complete the last two years of Al Franken's term. State Sen. Karin Housley is carrying the party's hopes in that race against Democratic Sen. Tina Smith.
For AP's complete coverage of the U.S. midterm elections: http://apne.ws/APPolitics
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