A Washington Post-ABC News poll offers conflicting forecasts for the 2018 midterm elections, with voters clearly preferring Democrats in control of Congress to check President Trump even as Republicans appear more motivated to show up at the polls.

A slight majority of registered voters — 52 percent — say they want Democrats to control the next Congress, while 38 percent favor Republican control to promote the president’s agenda, according to the poll.

Yet a surge in anti-Trump protests does not appear to have translated into heightened Democratic voter enthusiasm — a signal that could temper Democrats’ hopes for retaking the House majority next year.

Trump’s low approval rating, which dropped to 36 percent from 42 percent in April, could also be significant if it fails to improve in the next year.

The survey also suggests that a shifting electorate could end up propelling Democrats to major gains if voters who have skipped previous midterm elections show up to cast ballots in 2018.

The snapshot emerges just as Congress has hit a major stumbling block in its effort to repeal and replace the Affordable Care Act, with Republican leaders in the Senate falling short this week of the votes they need to advance their deeply unpopular bill.

Although the poll was conducted before the collapse of the health-care push, the results suggest fresh uncertainty as to whether Democrats can recruit strong candidates and mobilize voters despite negative views of the Republican agenda.

Republicans hold a 24-seat advantage in the House, and Democrats have pointed to the spike in activism, Trump’s unpopularity and voters’ general preference for Democratic congressional candidates as evidence that the majority could be in play.

The Post-ABC poll shows that Republicans hold the advantage in enthusiasm this early in the campaign cycle. A 65 percent majority of Republicans and GOP-leaning independents say they are certain they will vote next year, vs. 57 percent of Democrats and Democratic-leaning independents.

Among Americans who did not cast ballots in the last midterm elections, in 2014, Democrats and Republicans are about equally as likely to say they plan to vote in 2018 — suggesting there is not a disproportionate number of newly motivated Democrats ready to come off the sidelines next year.

Independents, meanwhile, prefer Democratic control as a bulwark against Trump’s agenda by the same 14-point margin as Democrats.

And then there is history: The party holding the White House, with few exceptions in the modern era, has tended to lose congressional seats in midterm elections.

“We have a unique opportunity to flip control of the House of Representatives in 2018,” Rep. Ben Ray Luján (D-N.M.), chairman of the Democratic Congressional Campaign Committee, wrote in a memo last month. “This is about much more than one race: the national environment, unprecedented grass roots energy and impressive Democratic candidates stepping up to run deep into the battlefield leave no doubt that Democrats can take back the House next fall.”

Democrats, however, already this year have suffered a series of losses in special elections for open House seats — none more crushing than their failure to win a suburban Atlanta race that drew more campaign and outside committee spending than any other House contest in U.S. history.

While Democrats came closer to winning these heavily Republican districts than in the past, the losses have spurred infighting and questions about how Democrats can best hone their strategy going into 2018.

The survey results suggest some reasons that Democrats have not been able to capi­tal­ize yet on voter antipathy toward Trump. For one thing, Americans who strongly disapprove of Trump do not appear to be any more motivated to vote than the average American.

Just over 6 in 10 of those who “strongly” disapprove of Trump’s job performance say they are also certain to vote in 2018 midterm elections. Overall, 58 percent of voters say they are certain to vote next year, while 72 percent of strong Trump backers are certain they will vote.

That result contrasts with a Post poll taken soon after the presidential election and the post-inauguration Women’s March that found Democrats more interested in increasing their involvement in politics.

Thirty-five percent of Democrats said then that they were more likely to become involved in political causes in the next year, compared with 21 percent of Republicans and independents. Nearly half of liberal Democrats and 4 in 10 Democratic women said they would become more engaged.

Now, it seems, the potential for a Democratic wave rides on whether the party can turn out voters who have tended to skip past midterm elections.

Democrats were more likely than Republicans to skip the 2014 congressional elections, and the poll finds that among those who sat out 2014 and now say they are certain to vote in 2018, Democrats have a major advantage. By 64 percent to 30 percent, more prefer Democrats as a check against Trump than Republicans who will support Trump’s agenda.

On the other hand, there is evidence that Trump’s struggle to pass major legislation has not sapped Republicans’ motivation to turn out.

There’s no significant difference between Republicans and Republican-leaning independents who say Trump is making significant progress toward his goals as president and those leaning Republicans who say he is not. About two-thirds of each say they are certain to vote in midterm elections.

And despite Trump’s dismal approval ratings, only slightly more voters say their congressional vote will be to “oppose Trump” — 24 percent — versus the 20 percent who say they will vote to support him. Just over half of voters say Trump will not be a factor in their votes.

The poll did not ask a generic congressional ballot question — an indicator often cited by party strategists — but recent polls show that voters favor Democrats over Republicans for Congress by between six and 10 percentage points when asked whom they would rather vote for.

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A report by the University of Virginia’s Center for Politics last month suggested that if Democrats maintain at least a six-point advantage on this question, they would be predicted to win enough congressional races to take control of the House in 2019.

While Democrats are heavily targeting the House in 2018, the Senate is seen as a tougher prize. Of the 33 seats in that chamber being contested, 25 belong to Democrats or independents who caucus with them. Of the eight GOP seats, forecasters and party campaign committees consider only two to be genuinely competitive.

The Post-ABC poll was conducted July 10-13 among a random national sample of 1,001 adults reached on cellular and landline phones. The margin of sampling error for overall results is plus or minus 3.5 percentage points and four points among the sample of 859 registered voters.

Scott Clement contributed to this report.