New Jersey Democrat Bob Menendez filed to run for reelection as an independent on Monday, a move that could be costly for Democrats trying to hold on to what has been a safe Senate seat.

Menendez, who is on trial in New York on corruption charges, could play the role of spoiler if a significant chunk of voters stick with him. Although Democrats are still favored to hold on to the New Jersey Senate seat, a Menendez candidacy could force the party to spend more money there when the party already is on defense nationally.

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New Jersey Republicans and Democrats hold their primaries on Tuesday but Menendez isn’t on the ballot. Democratic Representative Andy Kim is widely expected to succeed Menendez.

The senator’s filing appeared on the New Jersey Department of State’s website on Monday. His party is listed as “Menendez for Senate.”

Senator Gary Peters of Michigan, who’s running the Senate Democrats’ campaign operation, dismissed the notion that Menendez’ decision could hurt the party’s candidate, saying “the Democrat is going to win.” But his Republican counterpart, Steve Daines of Montana, smiled and quipped: “Keep your eye on New Jersey.”

Senator Cory Booker, a New Jersey Democrat, called his colleague “a tremendous senator for the state of New Jersey when it comes to delivering results” and a good partner, but said the focus now should be on the trial, not November. “He deserves a fair trial, where he gets to be judged by a jury of his peers,” Booker said.

Menendez, 70, has pleaded not guilty, and his defense has blamed his wife, Nadine, for withholding information from him about gold bars and other items federal prosecutors say were bribes to the senator for assorted official acts.

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Menendez, who was first elected in 2005, stepped down as chair of the Foreign Relations Committee after his indictment but continues to vote and attend classified briefings and committee hearings in the Senate. 

Senate Majority Leader Chuck Schumer has criticized Menendez’ conduct, saying it fell far below the standard of a U.S. senator, but has refused to address whether Menendez should face expulsion, be denied access to briefings or otherwise punished.