Thomas Kean

Representative Thomas Kean Jr., one of the most vulnerable Republican members of Congress, has missed more than a month’s worth of votes in Washington and has been absent from his New Jersey district as he deals with what aides have described as a personal medical issue.

The last vote Mr. Kean cast was on March 5. His extended absence comes as the House speaker, Mike Johnson, is reliant on a razor-thin majority to advance legislation vital to President Trump before the midterm elections in November.

Mr. Kean, 57, is also in the throes of a re-election campaign in one of the country’s most closely watched and competitive House races. Four Democrats are vying to replace him in the Seventh Congressional District, and primary ballots have already been mailed.

Harrison Neely, a campaign spokesman, said that Mr. Kean was “dealing with a personal medical issue” and would be “back to a full schedule soon.”

Mr. Neely declined to provide details about the nature of the health issue or estimate when Mr. Kean would return to public life in Washington and New Jersey.

“He’s going to be totally fine,” Mr. Neely said.

But Republican lawmakers and political consultants in New Jersey said that their concerns for Mr. Kean, a former state lawmaker, had grown in the last two weeks as calls and texts from friends had gone unanswered.

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