How the US Senate could swing to the Democrats

Pollsters looking ahead to Tuesday's elections predict the odds that Democrats will win enough seats in the US Senate to regain a majority are a little better than 50 percent, thanks in large part to the relatively high number of Republican-held seats at risk.

Of the 34 seats involved in this year's contest, 24 are presently occupied by Republicans who won six-year terms in the 2010 mid-term election, leaving the GOP with a wide flank to defend. And polling data suggest only two of the 10 up-for-grabs seats held by Democrats could feasibly flip to Republicans.

If the Democrats can pick up five additional Senate seats, they will emerge with a majority. But if the party's state-by-state Senate campaigning proves successful, it might have more to do with the race for the White House than anything else, according to political scholars.

"I think the local issues have really been swamped by the national campaign, and that, of course, is the risk you always have when there's a presidential contest at the top of the ballot," Peverill Squire, a political science professor at the University of Missouri, Columbia, tells The Christian Science Monitor in a phone interview.

Missouri is among eight states with Senate elections considered "toss ups," according to aggregate polling data compiled by Real Clear Politics. The others are Pennsylvania, Wisconsin, Indiana, Nevada, New Hampshire, Florida, and North Carolina.

Harry Enten, a reporter with data journalism site FiveThirtyEight, lists Senate races in two of those states – Pennsylvania and Wisconsin – as at least leaning toward the Democrats. The most interesting Senate contests to watch, he says, will be in three states: Nevada, New Hampshire, and especially Missouri.

"Missouri is perhaps the most interesting of the three because it's the state where we have the best chance of seeing one party win the Senate race and the other win the presidential race," Mr. Enten wrote.

Missouri's incumbent Sen. Roy Blunt (R) is defending his seat against Democratic challenger Jason Kander, Missouri's secretary of State, who is an attorney and Army veteran. Although the deafening presidential campaigns of Republican nominee Donald Trump and Democratic nominee Hillary Clinton have dominated political discourse in recent months, both Senator Blunt and Secretary Kander have raised a wide range of policy issues that matter to Missouri voters, Dr. Squire says.

"But I think it's probably been difficult for either Blunt or Kander to focus on state-level issues when everything is going to be wrapped around support for either Trump or Clinton," Squire tells the Monitor.

This compression of presidential and senatorial politics has cropped up in other key states as well. In Nevada, for instance, where four candidates are vying for the seat vacated by the retirement of Sen. Harry Reid (D), the Senate race seems to be more about presidential politics than anything else, says Kevin Banda, an assistant professor of political science at the University of Nevada, Reno.

"Issues probably don't matter all that much in terms of how people actually make up their mind when they are deciding whom to vote for. People just don't pay that much attention," Dr. Banda tells the Monitor. The fact that Nevada voters have a hard time ignoring Mr. Trump could hurt the Republican candidate for Senate, Joe Heck, while giving his main opponent, Democrat Catherine Cortez Masto, an edge, Banda adds.

Similarly, the Trump effect on New Hampshire's Senate race has spelled hardship for Republican incumbent Sen. Kelly Ayotte, who is neck-and-neck with Democratic challenger and Gov. Maggie Hassan.

"The biggest state-level concern has been actually Hassan's eagerness to associate Ayotte with Trump," Frank Cohen, an associate professor of political science at Franklin Pierce University in Rindge, N.H., tells the Monitor. Although the candidates have sparred over substantive matters of concern to the state's voters, including the economic recovery, job growth, and security concerns, the two candidates have frequently postured themselves in association and dissociation to presidential candidates.

Mary Malone, an associate professor of political science at the University of New Hampshire, says this interplay reflects the blurred lines between the state's priorities for its senators and its priorities in a president.

"I think that they're intertwined," Dr. Malone tells the Monitor. "I think that Trump's misogyny has really most certainly led to a lot of activism for women, and I think that his misogyny – especially when contrasted with electing the first female president – has really activated the women's vote."

Trump's spotlight has drawn attention to Senator Ayotte's record on women's reproductive rights, which includes voting to defund Planned Parenthood, Malone says. And the spotlight that follows Clinton, who has weathered a number of scandals during her campaign, directly affects Hassan's bid as well.

These three key states – Missouri, Nevada, and New Hampshire – will be among the most closely watched races as results pour in on Tuesday night, because they could be the key to unlocking a Democratic majority, Enten wrote for FiveThirtyEight.

"If Democrats win two of these three, it's difficult to see how they don't end up with at least 50 Senate seats," he wrote. "If they don’t, they’ll have to pick up at least one seat that appears to be trending away from them."

In the event that the Democrats net an additional four seats but fall short of a Senate majority – Enten predicts a 16 percent chance of that happening – then the Senate will be split evenly, 50-50, between Republicans and Democrats (counting two independents who caucus with the Democrats). In the case of a tie, the vice president casts the deciding vote.