With a growing Republican field for president (Sen. Lindsey Graham and former Texas Gov. Rick Perry joined the crowd last week), the Senate candidates have a vested interest in whom the party nominates. And with announced or likely candidates from some of these swing states – Gov. Scott Walker in Wisconsin, former Gov. Jeb Bush and Sen. Marco Rubio in Florida, Gov. John Kasich in Ohio –Senate aspirants could receive a boost.

Democrats, however, are confident that with Hillary Clinton on the ticket, they will have a strong advantage in these states.

“I think there’s a lot of excitement for Hillary’s campaign. I think that she’s going to have a major turnout effort and she’ll be all over the country in many places where we’re waging competitive Senate races,” said one Democratic operative involved with Senate campaigns. “Every state is going to be different. That’s kind of the thing about a Senate map … an issue might matter in one state where it doesn’t matter in another state, based on local politics. But excitement for Hillary and her candidacy, assuming she’s the nominee, will absolutely filter down and help our candidates.”

Nonetheless, Republicans aren’t resigned to a tougher climate simply because it’s a presidential year. One Republican operative said it’s “too simplistic” to view Senate races as a Democratic advantage in 2016. The operative pointed to Pennsylvania, where results have been mixed over the years. Republican Sen. Pat Toomey will likely face former Rep. Joe Sestak, whom he defeated in 2010. And though incumbent Democrat Bob Casey won in 2012, when Obama carried the Keystone State, longtime Republican incumbent Sen. Arlen Specter won in 2004 even though John Kerry carried the state at the top of ticket. Specter also won in 1992 when Bill Clinton won Pennsylvania, and Republican Rick Santorum won re-election in 2000 even though Al Gore carried the state over George Bush.