Rep. Rob Wittman (R-Va.), right, in 2016. (Steve Helber/Associated Press)

Democrats last won Virginia’s 1st Congressional District in 1974. It’s been reliably Republican ever since, with the current incumbent, Rep. Rob Wittman, winning reelection in 2016 with almost 60 percent of the vote.

But at least one measure of voter sentiment — a March 7 Wason Center generic ballot test – showed Wittman could be one Virginia’s most endangered Republicans, with 51 percent of respondents saying they would vote for a Democrat.

Granted, the 1st District sliver of the overall poll had a huge margin of error of plus or minus 10 percent. But the headline number is a shocker. Could Wittman really find himself swept away on a Democratic wave?

Anything is possible — except when you listen to the Democrats who hope to send Wittman down.

At a May 14 forum in Fredericksburg, the three Democrats — Edwin Santana, John Suddarth and Vangie Williams — shared their views on the issues.

They all want universal health care. They favor marijuana legalization. They are very much against the NRA. Williams suggested the organization should face a class action lawsuit and be disbanded.

And they all agree President Trump should be impeached.

Before a Democratic audience, and in advance of a Democratic primary, those points all play fairly well.

But how will they play outside the Democratic bubble? It matters, because taking out Wittman means running an unprecedently strong campaign that gets every conceivable break, and then some.

After court-ordered redistricting in 2016, the 1st District became, if anything, more Republican with the addition of Hanover County. But it’s also home to three “pivot counties” — Caroline, Essex and Westmoreland — that voted for Barack Obama in 2008 and 2012 but flipped to Trump in 2016.

Wittman won all three counties in 2016 and 2014. He won two of three in 2012. The one he lost in 2012 — Caroline — has moved steadily and strongly toward him since.

Sure, but how about after a year of Trump in the White House? Surely, that spectacle has eroded some GOP support.

In the 2017 gubernatorial race, Ed Gillespie won the 1st District 54-45 . Gillespie won Caroline by 9 votes, but he carried Essex and Westmoreland by more comfortable margins.

The point of this exercise: For a Democrat — any Democrat — to win the 1st District would require reconstructing the winning Obama coalition in those three pivot counties, assuming that coalition still exists.

But even if that could be done, it would leave a Democrat well short of victory. Winning would require making up ground in the district’s big population centers: Hanover and Prince William counties.

Hanover County, which Wittman won by almost 24,000 votes in 2016, appears to be a non-starter. Recall that this was the same county that, as part of the 7th District in 2014, voted 2-1 for Dave Brat. It did just about the same for Gillespie in 2017.

Ralph Northam won the district’s other population center, Prince William, handily in 2017.  Wittman doesn’t represent the entire county, but he has a good chunk of it. Wittman struggled here in 2016, winning by slightly more than 2,000 votes out of more than 81,000 cast.

Prince William, then, offers a Democratic candidate the opportunity to do well. Maybe not in the same league as Northam, but there’s a real possibility for a Democrat to win the dozen precincts Northam carried in 2017 that also went for Wittman in 2016.

Even if that happens, would it be enough for a Democrat to upset Wittman in November?

It’s a long shot for any Democrat not named Ralph Northam. It’s doubly so for a would-be Wittman-toppler who doesn’t have the financial resources and outside help to mobilize voters.

None of Wittman’s potential opponents has that kind of cash or outside support. And never mind Hanover County, which is unlikely to give much support to any Democrat campaigning as an unabashed progressive.

Despite the Wason poll, the real numbers say the Republican, Wittman, is likely to win once again.