Republicans are beginning to confront an atypical scenario in which they could hold on to what's now a razor-thin advantage in the Senate even as they lose their more comfortable House majority in the 2018 midterm elections.

Such an outcome would be highly unusual and shatter historic precedent but nonetheless is a result gaining feasibility based on the current political headwinds and next year's red-hued Senate map.

Backlash against President Donald Trump and the broader GOP among suburban, college-educated voters is threatening the party's hold on a host of congressional districts, even beyond the 23 that supported Hillary Clinton and a Republican representative last year. And yet at the same time, the party remains confident it can still convert a string of victories against Senate Democrats occupying largely rural, blue-collar states that favored Trump in 2016.

"We could end up with very different pressures in these races," says GOP consultant Brad Todd, who is advising Josh Hawley's challenge to Sen. Claire McCaskill in Missouri. "The map is hardening along its November 2016 lines. Places that the president carried in November 2016 are hardening to those holding back the president's agenda. Those states that were trying to push back the Obama years, they are hardening in their desire to do that. Places where the president underperformed for a Republican, those places are going to be tougher for us than they should be."

Once Sen.-elect Doug Jones of Alabama is sworn-in, Republicans will cling to a single-seat advantage in the Senate, making each of the 33 upper chamber races on the ballot next year crucial. In the House, Democrats need a gain of 24 seats to wrest back control, a turnover that now appears within reach.

In the last three midterm election cycles, the party not holding the presidency gained seats in both the House and Senate. More often than not, success for a party in one chamber begets advancements in the other.

But a handful of the Democratic senators who won their last six-year term in 2012 benefited from gaffe-prone, inept or uninspiring Republican opponents. McCaskill thumped former Rep. Todd Akin after she boosted the culture warrior in a messy three-way GOP primary and he later defended "legitimate rape." Sen. Joe Donnelly in Indiana defeated Richard Mourdock after Mourdock asserted during a debate that pregnancies from rape were "something that God intended." Meanwhile, Sens. Heidi Heitkamp and Jon Tester squeezed out narrow victories in the Great Plains against bland, lackluster congressmen.

Could each of these Democrats strike gold in drawing subprime opponents again? It's possible, but unlikely.

What's more is that Trump carried these four states by gaping double-digit margins, ranging from 19 points in Missouri and Indiana to 20 points in Montana and 36 points in North Dakota.

Even if Republicans incur losses in highly competitive contests in Nevada and Arizona, they have more opportunities to make up for them in Trump-voting states, like Florida, Ohio and West Virginia.

"Generally because of who's up and the states in the Senate, we have an advantage," says Charlie Black, a longtime GOP consultant, lobbyist and fundraiser. "We don't necessarily have the same advantage in the House districts."

The latest NBC News/Wall Street Journal survey hands Democrats their largest lead in congressional preference in nine years. Fifty percent of registered voters surveyed prefer a Democratic-controlled Congress, compared to 39 percent who want Republicans to stay in charge, an 11-point gap.

The last time Democrats enjoyed a double-digit advantage was just ahead of the 2008 election, when the party picked up eight Senate seats and 21 House seats.

But the same poll also found Trump's approval rating ticking up to 41 percent, a number that remains drastically low compared to his predecessors in their first year. But Black believes that "If he's at 41 percent nationally, he's probably in the high 40s in Missouri, Montana, Indiana and North Dakota."

"Senate races aren't as susceptible to the wave depending on which seats are up. This is very unusual to have all these Democratic seats up," Black adds.

"The map may bail out the GOP in what may be a very tough year," says GOP strategist Rob Jesmer, who headed the National Republican Senatorial Committee during the 2010 and 2012 cycles.

On the House side, Democrats appear to be expanding their list of targets every couple of weeks. To start, they'll need to flip a majority of the GOP-held districts carried by Clinton in the last presidential election. Seven are in California and four are clustered in the northeast corridor of Pennsylvania, New York and New Jersey. But some party operatives are becoming more bullish about expanding their sights into traditionally safe Republican enclaves. They include targeting Rep. Dave Brat in Virginia's 7th District, which encompasses a sliver of turf north and west of Richmond and the open seat of retiring Rep. Lamar Smith, in Texas' 21st District, which covers northern San Antonio. One Republican operative counts at least 30 GOP House incumbents as legitimately vulnerable to defeat and doesn't discount that figure increasing in the coming months.

"I see a historical trend cutting against us. ... We've got the wind at our face," House Speaker Paul Ryan of Wisconsin told The Wall Street Journal .

A second GOP operative working on a fleet of House races was more acerbic.

"I think we're totally f---ed," this operative says, requesting anonymity in order to protect his clients. He believes "the House is in greater jeopardy" at the moment due to midterm trends and Trump's unpopularity, but he isn't so sure Senate chances won't eventually dovetail along with them.

"History suggests that one party loses and one party wins," the operative says, adding, "The climate is worse today than it was in December 2009 [after President Barack Obama's first year in office] – like, way worse."

Jolted by unnerving losses in Alabama and Virginia, Republicans are now betting almost entirely on being able to tout tax cuts as their lifeline to saving their majorities.

"A lot's going to change with the tax bill and its impact on the economy and people's take home pay by next November," Black says, predicting that voters will see more spending money in their wallets by February or March.

Asked why the sweeping legislation remains unpopular with the majority of the public, Black, displaying a flash of frustration, retorts, "It's underwater because the damn press has been out there for a year saying it's for the rich, and then the Democrats said it."