Representative Denny Heck, Democrat of Washington, said on Wednesday that he would not run for re-election in November in part because the impeachment hearings, in which he has participated as a member of the House Intelligence Committee, had left him “weary.”

In a blog post on Medium, Mr. Heck listed the aspects of his job that he has “loved,” but said that “part of me is also discouraged.”

“The countless hours I have spent in the investigation of Russian election interference and the impeachment inquiry have rendered my soul weary,” wrote Mr. Heck, who was first elected to Congress in 2012. “I will never understand how some of my colleagues, in many ways good people, could ignore or deny the President’s unrelenting attack on a free press, his vicious character assassination of anyone who disagreed with him, and his demonstrably very distant relationship with the truth.”

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Mr. Heck represents a left-leaning district centered on Washington’s state capital, Olympia. As a member of the House Intelligence Committee, he participated in the televised impeachment hearings last month.