The Senate will cancel most of its annual August recess, Majority Leader Mitch McConnell told senators Tuesday, an election year move that will force vulnerable Democrats to shuffle their campaign schedules.

The Senate will now recess for one week in August instead of four, said McConnell (R-Ky.). He made the announcement in a closed-door lunch with Republican senators, according to several people familiar with his comments who spoke on the condition of anonymity.

His decision had been widely anticipated in the Senate Republican Conference. Some GOP senators sent a letter to McConnell last month urging him to keep the chamber in session to vote on judicial and administration nominations along with legislation, and Senate leaders have said the appetite to stay in town has grown in their ranks.

“We have a lot of important work to do,” McConnell said after the lunch. He said that to make progress on spending bills and nominations, “it’s necessary for us to be here in August and to do our work.”

The additional workweeks in August mean that endangered Democratic senators on the ballot will face a dilemma: Stay in Washington and attend to Senate business during time they could otherwise use to campaign back home, or remain in their states and face criticism that they are shirking their responsibilities in government.

The new schedule could also enable their Republican challengers — many of whom hail from the private sector or state government — to have the states to themselves during the late-summer stretch.

The House still plans to be out of session in August.

Democrats are defending 26 Senate seats this year, including two represented by independents in Vermont and Maine, and 10 in states Donald Trump won in 2016. Republicans have nine incumbents on the ballot.

The new August schedule is problematic for one vulnerable Republican: Sen. Dean Heller (Nev.), who is facing a reelection contest in a state Hillary Clinton won in 2016.

Republicans are working with the narrowest of majorities as Sen. John McCain (R-Ariz.) undergoes treatment for brain cancer in his home state. Democrats need only one senator to be present while the Senate is in session to object to GOP plans and throw up procedural hurdles.

Senate Democratic leaders said they welcomed the additional time to address health-care costs, including prescription drug prices. “I think if we can actually get some things done for the American people, that’s a good thing,” said Sen. Chris Van Hollen (Md.), chairman of the Democratic Senatorial Campaign Committee.

After a roller-coaster 2017 for the Republican-controlled Senate, which failed to repeal and replace the Affordable Care Act but later passed a sweeping tax bill that became law, GOP leaders have set a more modest agenda for the months leading up to the midterm elections. The Senate has mostly been focused on confirming executive branch nominees and judges.

Senate Republicans’ priority in the midterms is trying to keep control of the chamber. They hold a slim 51-to-49 advantage.

Trump’s low approval ratings and the swirl of controversy around the White House have Republican strategists worried about the party’s standing headed toward the fall. With every House seat up, many Republicans have privately concluded that their majority on one side of the Capitol may be all but gone.

A more favorable Senate map, though, has given them greater confidence about holding on to the upper chamber of Congress.

The president remains popular in many ruby-red states, including Indiana, where he campaigned for the Republican Senate nominee, Mike Braun, and bashed Democratic Sen. Joe Donnelly.

Other Democratic senators running in states Trump won include Heidi Heitkamp (N.D.), Joe Manchin III (W.Va.), Claire McCaskill (Mo.) and Jon Tester (Mont.).

Last year, McConnell announced in July that he was cutting the 2017 August recess in half. At the time, the party was trying to undo the ACA. Ultimately, he gave senators more time away.

Asked Tuesday if he was trying to leverage an agreement with Democrats on nominees in exchange for restoring some recess time, McConnell dismissed the possibility of altering his plans.

“I’m all for cooperation, but if you look at the amount of work that we have to do, it’s inconceivable to me that we can’t use these weeks,” said McConnell.

Paul Kane contributed to this report.