Republicans have their largest House majority since the Great Depression, thanks to sweeping electoral gains over the last six years. But Donald Trump’s rise has led to concerns about the fate of Republican candidates down the ballot this fall and whether his divisive candidacy and lack of Republican unity will cost the GOP seats in Congress.

Democrats have enthusiastically tied Republican lawmakers to Trump for months, and the hypothetical Trump ticket became a reality last week when the billionaire businessman all but secured the Republican nomination earlier than most expected.

Democrats are increasingly bullish about their chances to take back the Senate, where Republicans now dominate 54-46, with Trump atop the Republican ticket. The challenges for Democrats in the lower chamber, however, where Republicans outnumber them 246 to 188, are much steeper. They hope a landslide win by Hillary Clinton, their likely presidential nominee, would lead to significant gains in the House, but plenty would have to break their way to have a legitimate shot at retaking the chamber.

Democrats have made their strategy clear: link every Republican to Trump at every opportunity. At a press conference Wednesday, Minority Leader Nancy Pelosi pointed out Trump’s controversial and offensive statements, comparing them to rhetoric from House Republicans, arguing they are inextricably linked regardless of whether individual members support their party nominee. Asked afterwards whether Democrats are in a position to regain their majority, Pelosi answered, “Of course.”

“I think if the election were today, we could,” Pelosi told RealClearPolitics. “It’s not today, but we want to keep growing our ground game and getting out our message — mobilization on the ground, messaging in the air — to do that. But I think we have plenty of opportunity now."

Republicans in competitive races have taken different approaches to Trump. Some, like Florida Rep. Carlos Curbelo and Illinois Rep. Bob Dold, have said they will not support him. Others, like Virginia Rep. Barbara Comstock and Arizona Rep. Martha McSally, have taken a tactic similar to Speaker Paul Ryan’s and said Trump has not yet earned their support.

Despite concerns over a fractured party, Republicans are confident that because of favorable district maps and their massive gains during the Obama administration, even a Trump drubbing wouldn’t cause them to lose the lower chamber. Many in the GOP also push back on the notion that Trump’s candidacy will result in a Democratic landslide, citing his surprising success during the primary and Clinton’s high unfavorable ratings as evidence that he could be more competitive than expected.

Rep. Greg Walden, chairman of the National Republican Congressional Committee, told RCP in an interview that while he understood Trump’s deep unpopularity, GOP members were not “running in a vacuum,” and there’s more to the election than the effect Trump’s candidacy might have.

“I’m very comfortable where we’re at,” Walden said. In a reference to Democrats’ tendency to turn out in bigger numbers for presidential elections, Walden added: “I also fully understand how difficult campaigns are for Republicans in presidential years, and what I’m telling you is we’re ready for the battle and look forward to engaging."

Both sides also acknowledge that with six months to go before the election, House races are far from settled and the political environment could shift drastically before voters head to the polls.

If current trends continue, however, Democrats may have an opportunity to win substantial gains down the ballot. In the most recent RCP average, Clinton leads Trump by 6.4 percentage points. That lead could increase, decrease or disappear before November, but it’s a positive sign at this point for House Democrats. Data from recent elections indicate that very few voters split their tickets, voting for one party in the presidential race and another down the ballot. If this pattern holds, presidential performance will be intricately linked to how House candidates will fare this November.

Republicans hold 26 seats in districts that Obama won in 2012 – and 28 more where Mitt Romney won with less than 53 percent of the two-party vote. If Democrats won most of the seats that leaned heavily for Obama and even half the seats that leaned somewhat more Republican, they would be in a position to put the House majority in play.

Republicans, however, insist that ticket splitting is not a lost practice and believe it will be critical to their races this fall. Walden pointed out that because they hold so many seats in districts that Obama won in 2012, GOP members are well practiced at running ahead of their presidential candidate.

“There are only five Democrats in seats that Mitt Romney carried,” Walden told RCP. “If somebody has got a bad track record of bringing people across, it’s the other side of the aisle. We’ve got 26 members that have figured out how to win crossover voters."

In a swing district in Illinois, for example, Rep. Dold is facing a challenge from former Rep. Brad Schneider, a Democrat who defeated Dold in 2012 only to lose to him in a 2014 rematch. A recent internal poll conducted for Dold showed him with a 48-41 lead over Schneider despite Clinton having a 16-point edge over Trump in that district. Democrats dispute Dold's lead, however, and say a DCCC poll from early April showed Schneider with a 9-point lead over Dold.

Walden did say, however, that having so many candidates in districts that went blue in the last presidential race put Republicans “out over our ski tips a little bit” in terms of protecting seats this year. But he spun that as a positive, indicating that most vulnerable members were acutely aware of the political headwinds they would face this year.

Rep. Tom Cole, who chaired the campaign committee in the 2008 election, said his party is vastly more prepared than it was when it lost the majority in 2006 and lost seats again two years later. He said vulnerable incumbents are going home more, connecting with constituents and fundraising at a much better rate. He pointed to the fact that no Republican incumbent has lost a primary this year as evidence they’re prepared for a tough cycle.

“That suggests, again, excellent preparation,” Cole said. “It also suggests that people are able to discriminate between what they feel about Congress and how they feel their individual member is doing."

Democrats, on the other hand, have worked since the beginning of this cycle to put themselves in a position to take advantage of the tailwind their party has in presidential election years, which gives them confidence they can make substantial gains if an anti-Trump wave occurs. They have recruited candidates in about 80 congressional districts held by Republicans, according to a Democratic Congressional Campaign Committee aide, and they expect 40-50 of those could potentially be competitive.

They have highlighted 28 candidates in their “red-to-blue” program, candidates they believe have demonstrated an ability to make their race competitive. They’ve also been willing to endorse in Democratic primaries, trying to highlight candidates who they think would have a better shot at winning in November.

That hasn’t worked in every case, including this week in West Virginia’s 2nd Congressional District, where the DCCC-backed candidate, military veteran Cory Simpson, lost the primary to former state Del. Mark Hunt (though this district would have been very difficult for Democrats to win regardless of the candidate.)

Still, Democrats believe they have laid the groundwork to take advantage of a beneficial electoral climate. Rep. Ben Ray Lujan, chairman of the DCCC, said in an interview with RCP that the committee has taken a harder look at voter data and built a strong field operation in competitive districts much earlier than in previous cycles.

It isn’t necessarily about putting new districts on the map, according to a DCCC aide, because redistricting has made certain seats impossible for Democrats. Instead, it’s about tilting toss-up races in favor of Democrats, and bringing districts that lean Republican or were much more difficult for Democrats to compete closer in to the toss-up column.

“Many of these races are already competitive … ” Lujan said. “What Donald Trump has done is make these even more competitive and make districts that were out of reach in reach now.”

Republicans scoff at the notion that Democrats are in a position to make sweeping electoral gains, regardless of the top of the ticket or political climate. A spokeswoman for the Republicans’ campaign committee pointed to six districts – four of which are in the “Patriot Program” for vulnerable members – where Democrats have failed to recruit what Republicans view as viable challengers.

“I’ve yet to see the list of 30 Democrats that are going to take out 30 Republicans,” Walden, the NRCC chair, told RCP. “They’re making claims in seats where frankly, they’ve not even recruited a candidate, or one that would get to the B-level. I hear these claims and spin out there; I just don’t see it backed up by the reality of what’s going on."

To put the House majority in play likely would require a landslide victory by Clinton in the presidential race as well as a failure by most Republican candidates to separate themselves from Trump – neither outcome a sure thing by any stretch. Though Clinton does lead in current polling, there are still six months, two party conventions, three presidential debates and any number of other unpredictable events that could change the calculus before November.

James Arkin is a congressional reporter for RealClearPolitics. He can be reached at jarkin@realclearpolitics.com. Follow him on Twitter @JamesArkin.