– After months of confidence that public discontent with President Donald Trump would lift Democrats back to power in Congress, some party leaders are fretting that their advantages in this year’s midterms are eroding amid a shifting political landscape.

Driving their concerns are Trump’s approval rating, which has ticked upward in recent weeks, and high Republican turnout in some recent primaries, suggesting the GOP base remains energized. What’s more, Republicans stand to benefit politically from a thriving economy and are choosing formidable candidates to take on vulnerable Democratic senators.

One of their biggest sources of anxiety is the Senate race in Florida, where some Democrats fear that three-term Sen. Bill Nelson has not adequately prepared to defend his seat against Gov. Rick Scott, a well-financed former businessman hand-picked for the race by Trump. Scott and Nelson are close in early polls.

“I’m concerned about the race. I think everybody is,” said Ione Townsend, the Democratic Party chair in Hillsborough County, home to Tampa. Townsend said it will “be hard to compete” with Scott’s money.

The growing alarm about Nelson, one of 10 Democratic senators running this year in a state won by Trump in 2016, prompted the Senate’s top Democrat, Chuck Schumer to sound the alarm a few months ago in a private meeting in which he pleaded with Nelson to step up his efforts and hire a campaign manager, which he did not do until March, according to people familiar with the conversation.

In West Virginia, where Trump won by about 42 points and Republicans gave the president credit last week for urging voters to reject the primary candidacy of a former coal executive who had served jail time, Democratic Sen. Joe Manchin III acknowledged that Trump’s popularity in the state is a major boon for the Republicans.

“The more he can stay out of West Virginia and direct his energies elsewhere would be helpful,” Manchin said.

Democratic worries are mounting in the House, as well, where the party has been more confident of gaining the 23 seats it needs to retake the majority. Democrats are picking strong candidates in dozens of GOP-held suburban districts where Trump has lost significant support, but recent surveys suggest the races may be tightening.

High point

Trump’s approval is now at the highest point it has been all year, measured by Gallup in early May at 42 percent, a 5-point increase from the start of 2018. Meanwhile, the Democrats’ advantage when voters are asked which party they want to control Congress has shrunk, from 10 points in December to just 6 now, according to a Washington Post average of recent quality polls.

And Republicans are showing signs they will fight for the House, with GOP megadonor Sheldon Adelson agreeing to give $30 million to the Congressional Leadership Fund, a super PAC backed by Speaker Paul Ryan, according to a person familiar with the donation.

“I think anyone who was proclaiming victory a couple of months ago was premature,” said Rep. Daniel Kildee of Michigan, who is a member of the leadership team of the Democratic Congressional Campaign Committee. “I think the president’s standing obviously has some impact.”

Republicans still have plenty of reasons to worry. While Trump’s numbers have improved, his standing is still historically low for a first-term president and his administration continues to face scandals and chaos, as well as the expanding inquiry by Special Counsel Robert Mueller into Russian interference in the 2016 election.

History shows a president’s first midterm does not usually go well for his party. And recent special election results signal a strong year for Democrats, including their stunning win in the Alabama Senate race and the victory this year by a Democrat in a Pittsburgh-area district that Trump had won by 20 points.

Republican leaders, many of whom were previously uneasy about Trump and his brand of nationalistic politics and had clashed with him early in his tenure, have in recent weeks embraced the president, in large part because the party’s success could hinge on keeping his base fired up.