President Donald Trump’s net approval rating has dropped in all 50 states since his first month in office, but he remains relatively popular in several key states with competitive Senate races this year, according to surveys released Wednesday.

That could bolster Republican hopes to knock off vulnerable Democratic senators up for re-election and retain or even grow the GOP majority in the upper chamber of Congress.

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The outcome of those contests could not only decide control of the Senate but also determine whether the GOP has a positive counterstory on Election Day to balance what most experts currently believe will be losses in the House of Representatives.

Much of Trump’s erosion stems from the fact that the share of voters who disapprove of him has increased across the country. But the president is above water in key states, according to polling conducted monthly by Morning Consult in all 50 states and the District of Columbia. Consider:

  • In Missouri, where Democratic Sen. Claire McCaskill is a top Republican target, 50 percent of voters approved of Trump in May. That is down 3 percentage points from January 2017, when Trump assumed office. His net approval stands at 5 points. McCaskill’s RealClearPolitics polling average over Republican challenger Josh Hawley is a statistically insignificant 1.7 points.
  • In West Virginia, Trump’s approval rating was 62 percent, unchanged from January 2017. Democratic Sen. Joe Manchin faces a tough re-election fight against Republican Evan Morrisey. In two public polls last month, Morrisey led 1 by 2 points and trailed another by 13 points.
  • In North Dakota, Trump’s approval rating was 51 percent, down from 56 percent in January 2017. Democratic Sen. Heidi Heitkamp faces Republican Kevin Cramer, who secured the nomination Tuesday. In a hypothetical matchup, Heitkamp led Cramer by 3 points, according to a February Gravis poll.
  • In Montana, where Democratic Sen. Jon Tester is up for re-election, Trump had a 50 percent approval rating. That is down 6 points from January 2017. The president’s net approval in May was just 3 points, smaller than many other states with competitive Senate races. The president could make a special effort to knock off Tester, whom he blamed for sinking his nominee to run the Department of Veterans Affairs.
  • In Florida, where Democratic Sen. Bill Nelson drew a top-shelf opponent in Republican Gov. Rick Scott, Trump had the backing of 50 percent of the voters. That was down 6 points from January 2017 but still 5 points above water. Nelson has a lead of 1.4 points in the RealClearPolitics polling average, but Scott has led the past two surveys.
  • In Indiana, 52 percent approved of Trump, down 3 points from January 2017 but a 7-point net approval. That could bolster Republican Mike Braun’s effort to defeat Democratic Sen. Joe Donnelly. Braun led by 1 point in a Gravis poll last month.

Eric Ostermeier, a political science researcher at the University of Minnesota and founder of Smart Politics, said the qualify of candidates matters more than presidential approval ratings.

“It’s obviously a useful guide for a departure point for beginning to handicap these races. But it’s not a suitable substitute for an analysis of candidates and campaigns.”

“It’s obviously a useful guide for a departure point for beginning to handicap these races,” he said. “But it’s not a suitable substitute for an analysis of candidates and campaigns.”

Still, Ostermeier added, Republican candidates benefit — all things being equal — if Trump is popular, and vice versa. He said the president’s approval rating is a proxy for overall Republican sentiment in a state. He noted that voters are much less likely to split their votes — supporting a president of one party and a congressional candidate of another — than they were a generation ago.

Ostermeier said it would be unusual if Republican candidates won in states like Pennsylvania and Ohio — where the president is less popular — but lost in Indiana and Missouri.

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“If you’d say, ‘Well, that doesn’t make sense,’ then these numbers do mean something,” he said.

The Morning Consult polls suggest that Trump will be of less help in states where Republicans are on the defensive. His approval rating was 49 percent — with a 47 percent disapproval rating — in Arizona. GOP voters later this year will choose a nominee to replace unpopular, retiring Republican Sen. Jeff Flake. It is one of the few Democratic targets on an otherwise difficult 2018 map.

And Trump is under water — 49 percent versus 47 percent — in Nevada. Republican Sen. Dean Heller, who has had a complicated relationship with Trump, likely is the most vulnerable incumbent GOP senator this year.

PoliZette senior writer Brendan Kirby can be reached at [email protected]. Follow him on Twitter.