House Minority Leader Nancy Pelosi D-Calif.) speaks at a news conference to unveil congressional Democrats’ “A Better Deal” economic agenda, part of their 2018 midterm strategy. (Aaron P. Bernstein/Reuters)

Voters say they prefer Democratic candidates for the House of Representatives over Republicans by the widest margin in over a decade, according to a new Washington Post-ABC News poll — a fresh sign of trouble for the GOP majority one year before the midterm elections.

But Democrats’ effort to convert widespread disapproval of President Trump into victories in 2018 could be undercut by lower turnout, with Republicans expressing just as much motivation to vote in next year’s elections.

A slim 51 percent majority of registered voters say that if the election were held today, they would vote for or lean toward the Democratic candidate in their congressional district, while 40 percent say they would choose the Republican.

That’s the biggest spread in a Post-ABC survey since October 2006, just weeks before a midterm in which Democrats won back control of the House and Senate amid deep dissatisfaction with then-President George W. Bush and the Iraq War.

In recent history, regardless of the political climate, Democrats have tended to hold an advantage on this "generic ballot" question, which does not name specific candidates. On the eve of the 2014 and 2010 midterms, both banner elections for the GOP, Post-ABC surveys found Republicans trailed Democrats by three and five percentage points among registered voters, respectively. Those margins flipped in Republicans' favor among the smaller population of likely voters who were more motivated to turn out. The latest Post-ABC survey does not measure likely voters given that the election is still a year away.

Still, an edge of 11 points, even among registered voters, is an encouraging sign for Democrats a year before Trump’s first midterm — an election cycle that historically has been unkind to the sitting president’s party.

The findings come as congressional Republicans are trying to rehabilitate their brand after months of infighting and a failure to produce any major legislative achievements despite controlling the House, Senate and White House.

This fall, they embarked on a do-or-die push to rewrite the nation’s tax laws, believing that a successful effort will give them a much-needed political boost headed into the midterm campaign. If they fail, many in the party fear, they could see their congressional majorities wiped out.

The GOP is also contending with unwelcome distractions, most notably an investigation into potential Russian collusion with Trump campaign officials that has already resulted in criminal charges against three former campaign aides.

An early slate of GOP retirements also has complicated the party's effort to retain its House majority. In some key swing districts, Republicans will not carry the advantage of incumbency.

The Post-ABC poll finds Republicans are more unified in support of their party’s congressional candidates than about Trump’s job performance. While 76 percent of Republican-leaning registered voters approve of Trump, a larger 88 percent say they would vote for the Republican House candidate in their district if the election were held today. That level of unity is on par with 90 percent of Democratic-leaning voters who support their party’s candidates.

Democrats face their own challenges. They have yet to resolve divisions stemming from the 2016 primary between supporters of liberal insurgent Sen. Bernie Sanders (I-Vt.) and establishment backers of former secretary of state Hillary Clinton.

Those divisions have come roaring back to the center of the national political conversation in recent days, as former Democratic National Committee interim chairman Donna Brazile said in an excerpt from her upcoming book that Clinton's team had some day-to-day control over the party early in the campaign.

While Democrats are claiming energy and momentum in candidate recruitment and voter excitement, which they attribute to concerns about Trump and his party, they have failed to flip any Republican seats in the House special elections conducted since Trump was sworn in as president.

The Post-ABC poll suggests Democrats’ antipathy toward Trump has not translated to greater motivation to vote, with an identical 63 percent of Democratic-leaning and Republican-leaning registered voters saying they are absolutely certain to vote next year. The poll shows Democrats’ 11-point vote advantage shrinking to two points among people who voted in the 2014 midterm elections, underscoring one of Democrats’ main challenges next year: ginning up enough enthusiasm to prevent the spotty turnout of recent nonpresidential years.

The new poll shows that if Democrats can overcome those obstacles, they could have a fruitful 2018 election. The last time the party had such a stark advantage on the generic ballot was in late October 2006. Then, a Post-ABC poll showed Democrats leading Republicans 54 percent to 41 percent among registered voters.

Confidence about both major parties is not running high, the poll shows. Barely one-fifth of Americans, 21 percent, say they have a great deal or good amount of confidence in the Republicans in Congress to make the right decisions for the country’s future. Democrats fare just slightly better, with 27 percent saying they have confidence in the party, rising to 34 percent for Trump.

Trump also receives more intensely negative ratings, with 46 percent expressing no confidence at all in his decision-making, compared with 28 percent for both congressional Democrats and Republicans.

“Whenever there is a chance to do something against” Trump, said Patrick Johnson of Center Point, Ala., “I’ll be there.”

Johnson, who identified with the Democratic Party, said he expects that he will vote in the midterm election.

A Republican from Clifton, N.J., who only wanted to be identified as JP, said he doesn’t agree with Trump on everything, but “if you were to give me a hundred questions of him versus another Democratic nominee or potential candidate for any office, I would probably side more with” Trump.

The Democrats have an advantage over Republicans when it comes to relatability. By 46 to 37 percent, more say the Democratic Party represents their own personal values than the Republican Party. Just under half, 49 percent, say Democrats are more concerned with the needs of people like them; 36 percent say Republicans are more concerned.

About a month before the 2006 Democratic wave election, Post-ABC polling found Democrats had a larger 16-point advantage on the question of personal values and a 28-point edge on being concerned with people’s needs.

House Republicans hold a 239-194 advantage over Democrats in the House, with two vacancies. They have been the majority party there since 2011.

Anti-incumbent sentiment is similar to recent years, with a 60 percent majority saying they are inclined to look around for someone else to vote for next year. Just over one-quarter, 26 percent, say they want to reelect their representative in Congress.

While much of the emerging Democratic campaign message has centered on criticism of Trump, nearly half — 47 percent — of registered voters say the president will not be a factor in their decision at the ballot box if they vote next year.

Similar shares say they are motivated to vote for or against the president: 24 percent say one reason for their congressional vote will be to show support for Trump, while 27 percent say it will be to show opposition.

Still, voters’ perceptions of what their votes represent do not always correlate with the messaging strategies political parties deploy, and Democrats are expected to continue to hammer Trump and tether congressional Republicans to his controversial actions.

Post-ABC polls taken just before the 2010 and 2014 midterms, for example, showed that half or more voters said then-President Barack Obama was not going to be a factor in their choice. But Republicans featured Obama in their attacks against Democrats in both election cycles, and exit polling found no Democratic Senate candidate was able to outperform Obama’s approval rating in their state by more than nine percentage points.

Asked if Democrats’ winning control of Congress in next year’s elections would benefit rather than hurt the country, more see it as a positive than negative — but opinions are not resolute.

Fewer than four in 10 adults, 37 percent, say that if Democrats win, the country would be better off, higher than 26 percent who say the country would be worse off. But just about as many people — 34 percent — say it would make no difference.

Attitudes were similar over the prospect of a Republican takeover just before the 2010 midterms. A CNN/ORC poll in October of that year found 34 percent saying the country would be better off with them in power, while 28 percent said it would be worse, and 36 percent said it would make no difference.

The Post-ABC poll was conducted among a random national sample of 1,005 adults reached by cell and landline telephone Oct. 29 through Nov. 1. Overall results have a margin of sampling error of plus or minus 3.5 percentage points; the error margin is four points among the sample of 884 registered voters.

Scott Clement contributed to this report.