Mr. Walsh has not deleted his offending tweets, choosing instead to apologize for some of them. But his long, searchable trail means Mr. Walsh has spent the opening days of his campaign addressing his own record rather than mounting a coherent attack on Mr. Trump.

“I wouldn’t call myself a racist, but I would say, John, I’ve said racist things on Twitter,” Mr. Walsh said in an interview with the MSNBC host John Heilemann on Monday.

The difference between him and the president, Mr. Walsh said in an interview with ABC, is that Mr. Trump has “never apologized for anything he’s done or said.”

But asked by The Washington Post about a tweet in which he deployed an expletive used by Mr. Trump to describe Haiti, Mr. Walsh said that while his word choice was perhaps “a little too provocative,” he stood by his description.

Amid his media blitz, Mr. Walsh received bad news about his own radio broadcast. In a statement Monday, Salem Radio Network announced that it would exercise its right to cancel national distribution of Mr. Walsh’s radio program, effective in 30 days.

A company official said any broadcaster who becomes a bona fide candidate for office must leave the air or risk exposing stations to the Federal Communications Commission’s equal time provision, under which any other declared candidate could demand airtime equal to that afforded to Mr. Walsh.

Mr. Walsh has tried to portray himself as someone who experienced an awakening — a firebrand populist who contributed to a divisive climate that helped elect Mr. Trump, but who was now putting his own career on the line to atone for his role in the Trump ascendancy.