What do the numbers say?
One indicator of how a district will vote rests in the result of the presidential race in that district. The Republicans have an advantage here. There are 10 states Donald Trump won in 2016 that have an incumbent senator up for re-election: Florida, Indiana, Michigan, Missouri, Montana, North Dakota, Ohio, Pennsylvania, West Virginia, and Wisconsin.
There is one state Hillary Clinton won that has a Republican incumbent – Nevada.
Democrats are seen as behind the curve on the state level, as well. There are 13 states headed by Republican governors in which a Democratic incumbent is running for re-election – Florida, Indiana, Maine, Maryland, Massachusetts, Michigan, Missouri, New Mexico, Nevada, North Dakota, Vermont, West Virginia and Wisconsin.
Will the Democrats be able to flip any seats? Nothing is impossible, but taking back the Senate will not be easy.
Here’s a look at some of the Senate races that look to have the incumbent in some danger.
For the Democrats:
Florida – Democrat: Sen. Bill Nelson will be facing Florida Gov. Rick Scott in the Florida Senate race. Nelson has nearly $8 million in his coffers, but Scott has millions of his own. The race as it stands now is extremely close even though Scott only officially got into the race in early April. Nelson, pro-choice and an advocate of gun control, is a liberal in a state that sees a large number of retirees from northern states. That can work in the state whose unofficial motto is "the farther south you go the more north you get." However, Scott had little name recognition prior to his run for governor in 2010 and ended up taking the office and holding it for two terms. Trump won the state, albeit by only a few points, in 2016. The race is considered a "toss up" by Sabato's Crystal Ball at the University of Virginia, as well as by Inside Elections.
Indiana – Democrat: Sen. Joe Donnelly is running in a state where Trump earned 56 percent of the vote, about 30 percent more than Clinton. Republican strategists think Donnelly can be beat. Other political pundits seem to agree, though Donnelly has raised more money than the three candidates vying for the GOP spot on the ticket. Donnelly has been seen moving to the middle as the midterms approach. This week, along with Democrats Joe Manchin (W.Va.) and Heidi Heitkamp (N.D.), Donnelly voted for Mike Pompeo to be the new secretary of State. The three are all up for re-election in states Trump won. Donnelly voted against the tax reform bill passed in December, and some say that could hurt him come November.
Missouri – Democrat: Claire McCaskill has been a U.S. senator since 2006. She was the first woman elected to the U.S. Senate from Missouri, winning the seat once held by former President Harry Truman. There is a crowded field of Republican challengers, including state Attorney General Josh Hawley. Hawley could be hurt by the sex scandal enveloping GOP Gov. Eric Greitens. The primary is set for Aug. 7.
North Dakota – Democrat: Sen. Heidi Heitkamp is an incumbent Democrat running in a state where Trump won 63 percent of the vote in the 2016 election. She will likely face Rep. Kevin Cramer (R-N.D.), who is a close Trump ally who at first decline to get into the race, but later changed his mind. Her race is considered a toss-up by Sabato's Crystal Ball. Heitkamp told The Washington Post that Trump asked her to consider changing parties as she visited him at Trump Towers before he was inaugurated. Trump has campaigned for Cramer in the state.
West Virginia – Democrat: Sen. Joe Manchin has leaned toward supporting Republican issues several times since Trump took office. Trump won big in West Virginia, taking 67 percent of the vote, much of it perhaps due to Clinton's "We're going to put a lot of coal miners and coal companies out of business" remark. Manchin could face Don Blankenship, the coal baron who served time for conspiracy to violate mine safety and health standards in connection with the deaths of 29 miners killed in a cave in at the Upper Big Branch Mine. Blankenship faces two other Republicans, Rep. Evan Jenkins and state Attorney General Patrick Morrisey for the GOP spot.
Arizona – Republican: Sen. Jeff Flake announced his retirement last year. Democratic Rep. Kyrsten Sinema, Republican Rep. Martha McSally, former state Sen. Kelli Ward (R) and former Maricopa County Sheriff Joe Arpaio are all running for the seat. A recent poll showed Sinema ahead of the three GOP candidates by 6, 10 and 26 points, respectively. Trump beat Clinton by fewer than 4 points in Arizona, and that could help Sinema. The Cook Political Report as well as the University of Virginia's Center for Politics. Rates the race a toss-up.
Nevada – Republican: Sen. Dean Heller is a Republican running in a state where Hillary Clinton won. Nevada has a large Latino voting population and 12 percent of employees in the state are unionized. Those are two demographics that generally trend Democratic. In Heller's favor, he has campaigned hard against the Affordabe Care Act's "Cadillac tax," the high-cost plan tax that contains a 40 percent excise tax on employer plans exceeding $10,200 in premiums per year for individuals and $27,500 for families. The tax is scheduled to take effect in 2020. Last month, Heller's competition for the GOP primary, Republican Danny Tarkanian, announced that at Trump's request he decided to leave the Senate race against Heller. Tarkanian will be running for Nevada's 3rd Congressional District seat. The person in that seat now, Jackie Rosen, is Heller's likely opponent in November.
Sources: 270towin; Politico; Ballotpedia; University of Virginia Center for Politics