President Donald Trump’s approval ratings are generally in the tank, but a new NBC-Wall Street Journal poll suggests an important caveat: His numbers are stronger in key counties that he won in the 2016 election.

Pollsters queried voters in counties that had voted for former President Barack Obama but flipped to the GOP last year, and those in which Trump’s margin of victory was significantly greater than 2012 GOP nominee Mitt Romney’s results.

While Trump’s overall approval rating in the survey was 40 percent, it was 50 percent in those key counties in 16 states — Colorado, Florida, Georgia, Indiana, Iowa, Maine, Michigan, Minnesota, Missouri, Nevada, New Hampshire, North Carolina, Ohio, Pennsylvania, Virginia, and Wisconsin.

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Those are the states that likely will not decide control of the House of Representatives in next year’s midterms. The results of the poll indicate that Trump might not be the drag that Democrats expect in their quest to drive Republicans from power.

“*Potential* problem for anti-Trumpers in midterm elections,” tweeted RealClearPolitics elections analyst Sean Trende.

The poll is not unmitigated good news for Trump, however. Trende acknowledged in a follow-up tweet Monday that a 50 percent approval rating represents a significant erosion in his support.

“Well, if it is an average, that means he’s underwater in a big chunk of his own counties,” he wrote. “Embarrassed I missed that.”

The poll indicates a divergence in the Trump counties. His approval rating is 56 percent in “surge counties,” those where he outpaced Romney by a large margin. That is down from the average of 65 percent that he garnered during the election, but still healthy.

Trump fared worse in those counties that flipped from Democrat to Republican. Voters in those counties approve of Trump’s job performance by an average of 44 percent. The president won those counties by an average margin of 8 percentage points.

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Christopher Devine, a political science professor at the University of Dayton in Ohio, said polling generally has indicated that Trump has remained relatively strong among his base.

“It doesn’t seem like there is a wholesale collapse among people who were the backbone of his support.”

“That seems to fit with the impression I’m getting with other things … It doesn’t seem like there is a wholesale collapse among people who were the backbone of his support,” he said.

Devine said the “flipper” counties highlighted in the poll probably are more likely to be in congressional districts represented by Democrats, limiting the midterm impact of an erosion of Trump’s popularity. Many of those counties, for instance, make up the congressional district of Iowa Democrat Dave Loebsack. The same goes for Democratic Reps. Dan Kildee (D-Mich.) and Tim Ryan (D-Ohio).

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Devine said control of the House will turn on other factors as well, including the quality of candidates that Democrats recruit and the number of Republican incumbents who choose retirement over re-election.

Trump’s approval rating “has not budged” despite a torrent of bad news during the early months of his presidency. He questioned whether some analysts are overstating the president’s vulnerability. He pointed to the 40 percent overall approval rating.

“That’s not great,” he said. “It’s also not that far off from where his predecessors were.”