Republicans, struggling to uphold legislative campaign promises under a GOP president with historically low approval ratings, could be headed for a wipeout in 2018 unless they can start winning over voters by passing an appealing agenda.

The dismal warning comes from poll numbers that have grown increasingly dire for the GOP since it took control of the government in January. A particularly troubling poll number for Republicans, released last week by Quinnipiac University, found Democrats with a historic lead on the generic ballot.

The poll found voters prefer that Democrats win control of the House over Republicans by a margin of 54 percent to 38 percent.

"This is the widest margin ever measured for this question in a Quinnipiac University poll," Quinnipiac pollsters said in a statement.

Quinnipiac found voters "dislike Democrats less than they dislike Republicans," although neither party is particularly popular.

Disapproval is 71 percent for Republicans and 58 percent for Democrats, the poll found.

This month, the nonpartisan Cook Political Report shifted 20 GOP seats slightly in the direction of the Democrats, suggesting the minority party is gaining serious ground on Republicans ahead of the midterm elections.

"If the election for House were held next Tuesday, Republicans would likely lose their majority," Cook Political's House editor, David Wasserman, told the Washington Examiner. "Fortunately for them, it's still 18 months away."

Senate Republicans didn't fare much better in the Quinnipiac poll.

Voters said if Democrats won the Senate in 2016, the country would "be in a better place than it is now" by a margin of 41 percent, as compared with 27 percent who said it would be in a worse place and 30 percent who said it would be the same.

The popularity of the GOP majority is often tied to a Republican president, and so far Trump's numbers are hovering at or below 40 percent.

The fate of the Republican majority will also likely be determined by what they are able to accomplish before the campaign season kicks into high gear.

The two big agenda items — tax reform and healthcare reform — are moving along much slower than promised by Republicans.

A House-passed healthcare bill is now in the hands of the slow and deliberative Senate, which is likely to rewrite the whole thing.

House passage has not helped Republicans. Instead, it appears to have hurt them. Polls show the House healthcare bill is unpopular, with 44 percent opposed to it and only 31 percent in support of it.

That could change in the months ahead, political experts point out.

"A House vote on healthcare in May 2017 might be transformed by a much better plan from the Senate, assuming it can pass the House," University of Virginia political science professor Larry Sabato told the Washington Examiner.

Sabato, a key political poll watcher, agreed that Quinnipiac's 16-point generic ballot lead looks bad for the GOP, but he said it might be an outlier.

"That's by far the widest margin any poll I've seen has projected," Sabato said. "In fact, the polling average is just plus-six for Democrats, good but probably not good enough for Democrats to take the House."

The political map, meanwhile, favors Republicans in 2018. House Republicans enjoy a 23-seat majority, and only a "short list" of GOP seats are real targets for the Democrats, Sabato has pointed out, although that list has grown a little since the House passed its unpopular healthcare bill.

In the Senate, where Republicans have a two-seat majority, Democrats are more vulnerable in the midterm election. More than a dozen seats held by Democrats are considered vulnerable in 2018, as compared with only two GOP seats.

History favors Democrats, however. The party of the president lost congressional seats in nearly every midterm election in modern history, especially when voters viewed the president unfavorably.

Trump's decision to fire FBI Director James Comey is likely to further drive down the president's poll numbers, which were briefly on the upswing after his decision to bomb Syria to deter further chemical weapons attacks.

"Anybody who follows politics can see how Trump's controversial presidency could possibly deliver the House to the Democrats next year," Sabato said. "But it's far too early for any firm conclusions. Poll numbers can change rapidly, as we saw in the last 12 days of the election last fall."