A look at the battle for the U.S. House

Theoretically, Democrats could take back control of the House of Representatives. But right now, it doesn't look likely. That's had less to do with how the House races are shaping up and more to do with the tightening of the presidential race.

Republican-held seats still make up eight of 10 seats most likely to flip parties. But to win the House, Democrats need Hillary Clinton to win by a fairly big margin if they want to end Republicans' historically large majority. To do that, they need Donald Trump to tank.

The current breakdown in the House is 246 Republicans to 188 Democrats, meaning that to win control, Democrats need to turn 30 GOP seats blue.

• Nebraska Democratic Rep. Brad Ashford: Democrats say that Ashford is pulling away, with a recent poll showing him up over his Republican challenger, retired one-star Air Force Gen. Don Bacon, by double digits. But Republicans aren't giving up on this takeover opportunity; they think Ashford's win in 2014 was because of a weak incumbent rather than his strength as a candidate.

• Florida's open 18th District seat: This might be the most competitive Democratic-held seat on the map. Democratic Rep. Patrick Murphy is trying to unseat Republican Sen. Marco Rubio, leaving his Palm Beach-area seat for the taking. Businessman Randy Perkins, a Democrat, and Afghanistan war veteran Brian Mast, a Republican, are going after each other, and Republicans say they can turn voters off of Perkins. He recently told Mast, who is a war double amputee, to "be a man and stand behind your own ads." Democrats say their guy has enough money to withstand GOP attacks.

• New Hampshire Rep. Frank Guinta, a Republican: Guinta was badly weakened by admitting last year that he took illegal campaign contributions from his parents, but he somehow made it through the primary. Now he's facing his fourth straight matchup against former Rep. Carol Shea-Porter, a Democrat who isn't necessarily loved by voters either. Right now, the edge goes to Shea-Porter, given that Clinton is leading the state by an average 5 points, according to RealClearPolitics. The Democratic group House Majority PAC just put out a poll showing her up 10 points.

• Florida Republican Rep. Carlos Curbelo: A court-ordered redrawing of eight of Florida's gerrymandered congressional districts has tilted the overall map slightly toward Democrats. That's true for Curbelo's new Miami area district, which is Democratic-leaning and majority Latino. Curbelo is one of the few House Republicans who has said he won't support Trump. But Republicans thanked the campaign gods when former Rep. Joe Garcia won the Democratic primary. In 2014, an investigation accused his office of creating hundreds of fake absentee ballots. More recently, Garcia apologized for making a comment that Clinton "is under no illusions that you want to have sex with her."

• Illinois Republican Rep. Bob Dold: Dold is in the category of Republicans who could do everything right but still lose. His seat in the northern Chicago suburbs is one of the most Democratic districts Republicans hold this cycle. Former Rep. Brad Schneider, the Democrat whom Dold knocked off in 2014, wants his seat back. Given the state's heavy preference for Clinton, he has a decent shot.

• Minnesota's open Second District: Republican Rep. John Kline is retiring after more than a decade representing this Twin Cities suburban seat. Kline's potential successor is outspoken talk radio host Jason Lewis, who won his primary after questioning the need to have fought the Civil War and saying the "white population" has been "committing political suicide" and "cultural suicide." Democrats say that hospital executive Angela Craig is raising the money she needs to take this slightly Republican-leaning district.

• Nevada Republican Rep. Cresent Hardy: The moment Hardy, a political novice, won a surprise victory in 2014, Democrats started counting down to November 2016 for the chance to kick him out. But a RealClearPolitics average of polls showed that Trump is slightly up in this libertarian-leaning state. Democrats nominated one of the most polished candidates this cycle, state Sen. Ruben Kihuen.

• Iowa Republican Rep. Rod Blum: The district most likely to flip without the interference of redrawn borders is Blum's. He was a somewhat surprising surfer on the GOP's 2014 wave. And Blum has voted as if he were representing a district Mitt Romney won by 14 points. He faces former Cedar Rapids City Council Member Monica Vernon.

• Florida Republican Rep. David Jolly: First he wasn't running for re-election, betting on the Senate seat instead. Now he's back, and he's facing one of the most recognizable faces in Florida politics: former Gov. Charlie Crist, a Republican-turned-independent-turned Democrat who ran two failed statewide races and is now running in his hometown district, redrawn to favor Democrats. Jolly irritated the GOP when he criticized the party for its fundraising demands during a "60 Minutes" segment. This race could be a nail biter.