Democrats are on the verge of a major upset victory deep in Trump country, according to a new bipartisan poll shared first with TPM.

Democrat Conor Lamb leads Republican Rick Saccone by 48 percent to 44 percent in a survey conducted by RABA Research, a bipartisan firm. That would mark a huge upset in a conservative district that stretches from Pittsburgh to the West Virginia border that President Trump won by 20 points in 2016. It would give Democrats their first House special election victory of the Trump era on Tuesday night.

That marks the largest lead for Lamb seen in any public polling so far — but it’s not far from what other public and private polls have found in recent days and weeks on the race, most of which have found a margin-of-error race with Lamb having the momentum. Two other public polls of the race found each candidate with a three-point lead, and Republicans are privately sounding more than a little gloomy about Saccone’s chances on Tuesday.

Trump plans to campaign there on Saturday to try to goose GOP base turnout for Saccone, who has mightily struggled with fundraising and getting his name out there as GOP outside groups have had to pick up the slack with millions of dollars worth of TV ads. But according to the survey, the president is currently unpopular with the district’s most likely voters, with 48 percent of those saying they definitely or probably plan to vote in the race disapproving of his job performance to just 44 percent who approve. Similarly, the poll suggests a lopsided edge for Democratic enthusiasm: Though the district is fairly solidly Republican, 41 percent of those surveyed said they were Democratic and 40 percent identified as Republican.

That could be a sign that the survey’s sample is a touch too Democratic, and that its likely voter screen might be a bit too tight. But it could also be capturing the very real signs of a Democratic wave — a huge disparity in voter enthusiasm from one party to the other.

The poll of 707 interviews was conducted via an automated phone survey and an internet supplement for those who only have cell phones from March 6-8. Its margin of error is plus or minus 3.7 percentage points.

The full memo is below.