The poll finds that registered voters prefer Democratic candidates for the House over Republican candidates by 50 percent to 43 percent. That marks a slight decline from last month, when Democrats led on the generic congressional ballot by 11 points, and a bigger drop from August, when they enjoyed a 14-point advantage.

Democrats also have a 51-to- 44 percent advantage among likely voters identified by The Post. That seven-point margin, which is in line with other polls taken in the past two weeks, puts Democrats roughly within range of what they probably will need in the overall national vote for the House to capture a majority from the Republicans, based on calculations from previous midterm campaigns.

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However, there is no way to translate the national numbers into the district-by-district competition that will ultimately decide who controls the House in January. Democrats need a net gain of 23 seats to capture control of the House. Public and private polls of individual races conducted by candidates, political party committees, the media and others show many contests still within the margin of error.

Republican candidates in competitive House districts, almost a third of which backed Hillary Clinton in 2016, threaten to be dragged down by the president’s unpopularity. Presidents with approval ratings as low as Trump’s have generally suffered significant losses in midterm elections. But this president has shown over time that historical statistical benchmarks don’t always apply to him.

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Trump’s approval rating among all adults stands at 40 percent, holding steady from a poll in early October and slightly higher than his 36 percent rating in August. Those who disapprove account for 53 percent. Among registered voters, Trump’s approval is 44 percent, with disapproval at 52 percent, the best margin among this group during his presidency.

All midterm elections are a referendum on the incumbent president, and Trump has made this election about himself more than most presidents have, insisting in his campaign rallies that voters should approach the election as if he is on the ballot. But elections also tend to reflect views of the economy, and Tuesday’s provides a test of the tension between perceptions of the president and perceptions of the economy. Rarely has there been as great a distance between views about the economy and a president’s ratings as there is this year.

On Friday, the Labor Department’s monthly employment report produced a string of positive numbers: another month with the unemployment rate at 3.7 percent, the lowest in half a century; 250,000 jobs added to the workforce; and wages posting the biggest increase in almost a decade and faster than inflation.

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The Post-ABC News poll was conducted Monday through Thursday, the day before the employment statistics were announced, and records the most optimistic attitudes about the economy in nearly two decades, with 65 percent of all Americans rating the state of the economy as good or excellent and 34 percent offering a negative assessment. The last time optimism ranked so high was in January 2001.

Among registered voters, 71 percent say the economy is good or excellent, up from 60 percent in August. Those who give the economy positive ratings favor Republican candidates for the House by 54 to 40 percent, wider than the 49 to 42 percent margin in August.

Similarly, more than 8 in 10 adults say they are either doing about as well financially as they were before Trump became president (60 percent), or are doing better (25 percent). Just 13 percent say they are not as well off. That 13 percent figure is also among the lowest in 18 years; the last time it dropped that low was in the final year of President Bill Clinton’s administration, when a boom in technology fueled a rising economy.

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Republican candidates have tried to emphasize the economy in their campaigns, but they have sometimes been overwhelmed by presidential rhetoric and by sharp attacks by Democrats on the issue of health care, which have put them on the defensive.

The president has used the final weeks of the midterm campaign to hammer on immigration more than any other issue. He has warned of threats to the country from a caravan of Central Americans who are in southern Mexico and heading north. He has ordered federal troops to be deployed to the border in response.

Earlier last week, Trump promoted an incendiary video highlighting an unrepentant undocumented immigrant who killed two law enforcement officials. The video sought to make him a face of the migrant caravan, even though he is in prison, and to blame Democrats for his acts. Democrats in turn denounced the ad as racist.

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The president’s focus on immigration appears to have raised the importance of the issue in the minds of his party’s voters ahead of Tuesday’s voting. Since a Post-ABC News poll three weeks ago, the share of Republicans saying immigration is “one of the most important issues” in their vote has grown from 14 percent to 21 percent. The share of Democrats saying immigration is a top issue has dropped from 23 percent to 11 percent.

When all voters were asked which party they trust more to handle immigration, Democrats were slightly favored by 47 to 42 percent over Republicans. But on border security, which has been the principal focus of the president, Republicans are more trusted by 49 percent to 39 percent.

Those who rank immigration as one of the most important issues in the election favor Republicans over Democrats by 12 points when choosing a generic congressional candidate, though the gap among this group is tenuous given its large error margin. For those who say border security is one of their top issues, Republicans lead Democrats by 42 points on the House vote.

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Those groups who have shifted toward Republicans on the issues of immigration since early October include white men without college degrees, voters over age 65 and voters who live in rural areas — all staples of the coalition that elected the president two years ago.

Democrats hold a lead almost as large — 39 points — among those voters who rank health care as one of the single most important issues. They lead by 69 points among those for whom global warming is one of the most important issues and by 46 points among those who say reducing divisions in the country is a top issue.

Overall, 17 percent of voters consider health care and reducing the country’s divisions as among the single most important issues — about the same as the economy (15 percent) and immigration (14 percent). When looking more broadly at issues voters say are at least “very important,” health care and the economy top the list at 78 percent and 76 percent, respectively, followed by reducing political divisions, immigration, taxes, border security and global warming.

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Presidential approval correlates closely to how people vote and the poll underscores that relationship, with 87 percent of those who approve of Trump saying they support Republicans for the House and 88 percent of those who disapprove saying they prefer Democratic House candidates.

Another measure of the polarization of the electorate is the relationship between party identification and voting intentions. In this survey, 94 percent of Republicans and Republican-leaning independents favor GOP House candidates, and an identical percentage of Democrats and Democratic-leaning independents say they favor candidates from their party.

Gender and education continue to be dividing lines in the electorate. On the vote for the House, men are split 47 to 46 percent in favor of GOP candidates, while women back Democratic candidates by 54 to 40 percent. White women with college degrees favor Democratic House candidates by 16 points and white men with college degrees back the Democrats by 14 points. Among whites without college degrees, men favor Republicans by 39 points and women by 12 points.

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Young voters ages 18-39, who historically have turned out at much lower rates in midterm elections than older voters, show a wide preference for Democrats, by 58 to 35 percent. Those between age 40 and those over age 65 are nearly evenly divided.

Among those who say they are certain to vote or already have voted, Democrats enjoy a nine-point advantage, while those who say they probably will vote or that the chances are “50-50” tip toward Republicans by four points, with 10 percent undecided.

The Post-ABC News poll was conducted Oct. 29-Nov. 1 among a random national sample of 1,255 adults, with 65 percent reached on cellphones and 35 percent on landlines. Overall results have a margin of sampling error of plus or minus three percentage points; the error margin is 3.5 points among the sample of 1,041 registered voters and four points among the sample of 737 likely voters.