Washington (CNN) The Republican majority in the Senate -- and maybe even the House -- could be gone after this year's election.

But gridlock and dysfunction on Capitol Hill are here to stay.

With Donald Trump trailing in the polls, Hillary Clinton is increasingly turning her attention to down-ballot races -- particularly for the Senate, where Democrats are hoping to pick up at least the four seats they'd need to claim the majority if Clinton wins the White House.

A Democratic Senate could go a long ways to helping Clinton's White House be successful, especially if they can move along a Supreme Court nomination and high-profile legislation early in her administration. At the same time, the House is likely to be more conservative next year, and the 2018 Senate map is so brutal for Democrats that any majority is likely to be short-lived.

Endangered Republicans, meanwhile, are increasingly seeking distance from Trump and pitching themselves as checks to a Clinton administration.

The evolution in Republican candidates' messaging was on display Monday in New Hampshire, where Clinton sought to latch GOP Sen. Kelly Ayotte to Trump -- and tout Ayotte's Democratic challenger, Maggie Hassan, as someone who "unlike her opponent," stands up to the GOP nominee.

Ayotte, meanwhile, all but admitted Clinton is poised to win the White House.

"There's so much at stake in this presidential election: the Supreme Court, our national security, so many issues that matter to people of this state," Ayotte told CNN's Manu Raju in an interview . "And Gov. Hassan is going to essentially follow Hillary Clinton's lead on all of them, where I'm going to stand up to her when she's not taking us in the right direction."

But Republicans are discovering that a checks-and-balance message cannot solve down-ballot woes in every state. One GOP operative who tested an advertising campaign in Wisconsin and Pennsylvania that called for a counterweight to Clinton found that the Democratic nominee was simply too popular there for that strategy to succeed.

Nevertheless, GOP Sen. Pat Toomey distanced himself from Trump in a debate Monday night with Democratic challenger Katie McGinty in the Clinton-leaning state.

"Unlike Katie McGinty, I am not a hyper-partisan, reflexive ideologue who thinks he has to give blind obedience to his party's nominee," Toomey said.

How Democrats can capture the Senate

Democrats' chances of winning the Senate start with three states where polls have shown them solidly ahead: Wisconsin, Illinois and Indiana, where former Sen. Evan Bayh is attempting a comeback against GOP Rep. Todd Young, who's been buoyed by an influx of spending from outside groups.

Democrats are also targeting Ayotte, as well as Republican Sens. Richard Burr in North Carolina, Pat Toomey in Pennsylvania and Roy Blunt in Missouri -- where Democratic challenger Jason Kander's ad featuring him assembling an AR-15 assault rifle while blindfolded could be the cycle's most memorable.

If Trump were to totally collapse, Democrats hope to be within striking distance of Arizona Sen. John McCain and Florida Sen. Marco Rubio as well -- though both currently appear safe.

For Republicans, the only viable pick-up opportunity of the current cycle is in Nevada -- where Democrat Catherine Cortez Masto and Republican Rep. Joe Heck are batting for retiring Senate Minority Leader Harry Reid's seat in a race that could swing with the presidential contest there.

Still, even if Election Day tips heavily in Democrats' favor, it's unlikely to change much on Capitol Hill.

Democrats' opportunities for House pickups were limited by 2010 redistricting -- which means Republicans are likely to retain control of at least one chamber.

And if the party sheds some House seats, what's left would be a House GOP even smaller and more conservative -- with less room for Speaker Paul Ryan to cut deals with Democrats that cost him conservative votes.

On the Senate side, a President Hillary Clinton would not have the 60-vote majority that President Barack Obama entered office with and used to shepherd Obamacare into law. That would leave Senate Republicans with power to stymie bills favored by the majority.

On the campaign trail for Clinton Saturday, Obama urged voters not to follow Republicans advocating for divided government.

"Now their excuse for why they should be elected is, 'Maybe we did support Trump -- now we're kind of quiet about it -- but you should vote anyway because we'll check Hillary's power. We'll be a counterweight,'" Obama said. "No no no no. No."

GOP likely favored in 2018

As soon as the 2016 campaign ends, the 2018 Senate races will begin.

And for Democrats, that's a frightening prospect.

Already disadvantaged in midterm elections, when Republican voters tend to show up at the polls more reliably than Democrats, the party faces the prospect of defending five Senate seats in deep-red states: Indiana, Missouri, Montana, North Dakota and West Virginia.

Democrats also could face tough races in a swath of competitive states: Florida, Ohio, Pennsylvania, Virginia and Wisconsin.

So Democrats aren't eager to talk 2018 just yet.

In Indiana, where Bayh is trying to beat back a barrage of outside spending from GOP groups and John Gregg is trying to win the governor's seat currently held by Republican vice presidential nominee Mike Pence, Democratic first-term Sen. Joe Donnelly will be up for re-election.

"No one is focused on that at all right now. There's two weeks to go, and right now we're in the driver's seat," said Dan Parker, the former Indiana Democratic Party chairman.

"Even Joe Donnelly's crew is focused squarely on helping Evan and John Gregg win," he said. "Obviously winning a Senate race and the governor's race this year would be huge for Joe."

For Republicans facing what could be a dark Election Day on November 8, though, the 2018 Senate map offers reason for optimism.

"Republicans are still hoping to hold onto the majority this year, and it is still within the realm of possibility. However, even if the Senate were to go 50-50 or even 49-51 or 48-52, the playing field in 2018 is so favorable to the Republican Party that I would anticipate taking the majority back," said Scott Jennings, a GOP operative who ran a pro-Mitch McConnell super PAC in 2014.

"A dream scenario is, you hold at 51 this year, and then you try to pick up nine in 2018," Jennings said. "But even if you lose the majority this year, picking up seats in 2018 looks like a strong bet. So even if we're banished the to the wilderness, it should be a short-term trip."