“What all the pro-Trump people don’t understand is that conservatives for the past 20 years have been preprogrammed to go beat Hillary Clinton, and if they perceive him as an obstacle to doing that, they’re going to move on,” he said.

The conservative news media has always been somewhat conflicted over Mr. Trump, whose tax policies and positions on social issues do not entirely align with theirs. But for conservative commentators like Ann Coulter, who, like Mr. Trump, is focused almost entirely on stopping illegal immigration, the issue is not that Mr. Trump is losing the support of the conservative news media. It is that he never had unified support in this influential space in the first place.

“The anti-Trump G.O.P. media outlets have gone from blind sputtering hatred to angry contempt and now seem to have settled on impotent rage,” Ms. Coulter said.

News media like CNN also still rely on Mr. Trump to drive ratings, though he is less of a draw than he had been in months after he announced his candidacy. In an interview with CNN on Tuesday, Mr. Trump highlighted his position at the top of the field and showed no signs of toning down his bombast. “I’m not going anywhere,” Mr. Trump said. “I’m leading every poll. I’m going to win, and I’m going to make our country great again.”

But there are signs that many voters and commentators have at least started to move on. When Mr. Trump came out strong in the primary polls, the conservative radio personality Glenn Beck, who also owns The Blaze, a TV and digital news outlet, reached out to Mr. Trump’s office to arrange for him to come on the program. But Mr. Beck’s interest in Mr. Trump appears to have cooled. He has had Mr. Carson, Mrs. Fiorina and Mr. Cruz on his nationally syndicated radio program, but said he no longer had any interest in “the circus” of hosting Mr. Trump.

“I think he’s a schoolyard bully who does not reflect any of the values and principles that I see from Americans on both sides,” Mr. Beck said, expressing frustration that the anger Mr. Trump has tapped into is often associated with the Tea Party. “He’s not a Tea Party guy,” he said.

Mr. Trump has tried to use being shunned in the news media to his advantage. But he may have hurt his chances of reaching his voter base when he instigated an on-again, off-again public feud with Fox News — the highest-rated cable TV channel in the country, which holds enormous sway over Republican primary voters — and its chairman and chief executive, Roger E. Ailes.