Control of US Senate at Stake TuesdayControl of the U.S. Senate – and largely the success or failure of the next U.S. president's agenda – rests on just a handful of races nationwide that polls show are tightening in the final hours before Election Day 2020. Of the 35 U.S. Senate seats up for reelection Tuesday, seven are rated true toss-up races by the non-partisan Cook Political Report. Democrats need a net pickup of three seats if Democratic presidential candidate Joe Biden wins the White House or a net pickup of four seats if U.S. President Donald Trump is reelected to a second term, because if there is a 50-50 Senate, the vice president breaks the tie. Senate Republicans currently hold a 53-47 majority but have a numerically more challenging year since they are defending twice as many seats as Democrats this election cycle. Only one of the 12 Democrat-held U.S. Senate seats up for reelection this year is rated as leaning Republican. In the Alabama Senate race, Trump-endorsed former football coach Tommy Tuberville has been leading Democratic Senator Doug Jones for months. Trump's influence will be the deciding factor for most of these close toss-up races, says Michele Swers, a professor of American government at Georgetown University. "If he wins a state, it's very likely that his coattails could help pull over the person who's running for Senate. And if he's doing poorly in a state, that's a big hurdle that they have to make up," she said. Here's where a handful of key races stand: Iowa "This is where you really get a good signal of the dynamics of the national race affecting state-level races," said Casey Burgat, director of the Legislative Affairs program at the George Washington University Graduate School of Political Management. Trump won Iowa in 2016 by nine points, but the state is now considered a toss-up at the presidential level and incumbent Republican Senator Joni Ernst has been trailing Democratic challenger Theresa Greenfield in several polls. "It just speaks to the momentum on behalf of Democrats and nationalizing elections at the Senate level – where a traditionally red state – now they're having to pump money in at the presidential level, the Senate level, which will distract and take away from money from those states that Trump surprisingly won in 2016," Burgat said. In this heavily agricultural state, Ernst is tied to Trump due to her support for his trade wars with China that have had an impact on farmers. Both Ernst and Greenfield have touted their ties to farming, but Ernst stumbled in a recent debate when asked to name the current going rate for corn while Greenfield immediately answered a similar question about the price of soybeans. But Georgetown University's Swers says Trump's handling of the coronavirus is also having an impact on Ernst's race. "It's been difficult for her because she has dealt with the coronavirus pandemic. The governor of Iowa also is a Republican and she has not wanted to put in a mask order and hasn't been that heavy handed. There's a lot of spread of coronavirus in Iowa and I think Ernst is hurt by that," she said. North Carolina The most expensive U.S. Senate race in history – with more than $250 million in spending – has also been one of the strangest in its final month. North Carolina's incumbent Republican Senator Thom Tillis had to isolate after contracting the coronavirus in early October and his Democratic challenger Cal Cunningham has stepped back from the campaign trail after admitting to an extramarital affair. In a Real Clear Politics average of polls taken since those announcements, Cunningham still leads Tillis by an average of 2.5 percentage points. North Carolina has earned a reputation as a national bellwether due to its diverse demographics and mix of rural, urban and suburban voters. Swers says that national attention as a key presidential swing state, with competitive races up and down the ballot, has an impact on the Senate race. "They have the full panoply of competitive elections, which means that there's lots of other people who are out there on the ground, trying to get you to vote for Democrats or to get you to vote for Republicans," she said. "Both Biden and Trump and the super PAC supporting them are spending very heavily in the state." Swers said that Cunningham has likely made the calculation that less is more, in terms of campaign appearances, to control the damage from his revelation. Maine Incumbent Maine Republican Senator Susan Collins made her own calculation in the weeks before Election Day, casting the lone Republican vote against confirming Trump's Supreme Court nominee Amy Coney Barrett. While Collins said she was concerned about the confirmation falling so close to Election Day, analysts also say that decision was likely based on the challenge she faces from Democrat Sara Gideon. The former Maine State Representative raised millions from Collins' last Supreme Court vote, confirming Justice Brett Kavanaugh after a contentious 2018 confirmation process involving sexual assault allegations. Collins' vote led many in Maine to question her identity as an independent voice in the U.S. Senate. "There was no real way for Susan Collins to win here," said Swers, who notes that Collins must maintain the support of Trump's base in the northeastern state. "They're going to be very angered by the fact that she voted against Amy Coney Barrett, and they might be less enthusiastic about coming to vote for her. On the other hand, she's relied very heavily on moderate Republicans, women and moderate Democratic women to support her in the past, particularly pro-choice leaning women. And so those voters were particularly turned off by her vote in favor of Brett Kavanaugh." In the latest Emerson College poll, taken after the Supreme Court confirmation vote, Gideon leads Collins by six points. Georgia If control of the U.S. Senate comes down to a matter of one seat, that pathway will likely go through the southern state of Georgia, where there are two races this year. Because one of those races is a run-off, where the winner must command at least 50% of the vote, the final makeup of the Senate may not be known until that runoff election takes place on Jan. 5, 2021. Currently, a Real Clear Politics average of polls shows Reverend Raphael Warnock leading by 15.6 percentage points. But because there are two Republicans – incumbent Kelly Loeffler and Rep. Doug Collins – in the running, Warnock likely will not command the majority needed to win outright in November. "Because she was juggling Collins jumping into the race, Kelly Loeffler can no longer move to the middle. She's competing for the Trump supporters with Doug Collins. So, she's been moving to the right and running advertising about how she's more conservative than Attila the Hun, which is not something that's going to get your voters that are in the middle. It's a difficult spot," said Swers. In the other Georgia Senate race, Democratic challenger Jon Ossoff leads Republican incumbent Senator David Perdue by one percentage point in an average of polls collected by Real Clear Politics. Toss-ups Other toss-up races include Republican Senator Lindsey Graham, one of Trump's strongest supporters in the U.S. Senate, who is fighting off Democratic challenger Jaimie Harrison in the southern state of South Carolina. Harrison, former chair of the state's Democratic Party raised a record-breaking $57 million in the latest fundraising quarter. In Montana, a state Trump won by 21 percentage points in 2016, Democratic challenger Steve Bullock leads incumbent Republican Steve Daines by just one percentage point in an MSU-Billings poll conducted in mid-October.