“It is a common trait among those who ran privately held corporations,” said Ari Fleischer, who served as White House press secretary for George W. Bush and frequently defends Mr. Trump. “Their way is the only way. Their will gets it done. They’ve been successful against all odds, built something huge, and when they declare it so they expect everybody around them to make it so. That’s Donald Trump’s behavior, and that doesn’t always work in politics or in government.

“Politicians don’t operate the way he does,” Mr. Fleischer said. “Frankly, it’s put him at risk and put the Republican Party at risk, but it also allows him to take on China and do something of tremendous consequences that no politician would ever do. If Trump is successful, this will be a better country and a better world for it.”

Yet there is little evidence that President Xi Jinping of China, or any other foreign leader, is cowed.

And certainly not Speaker Nancy Pelosi. The president initially said he felt comfortable negotiating with Ms. Pelosi, but in interviews aired on Sunday, he sharpened his attacks on her and said her obstinacy on the border wall was damaging the country.

Mr. Trump has found that his lack of experience in politics and diplomacy, which require policy knowledge, team building and nuanced negotiating ability, has left him at a decided disadvantage despite his boasts about his deal-making prowess.

“He’s surrounded in these standoffs by people who have all those boxes checked,” said Timothy O’Brien, the author of “TrumpNation: The Art of Being the Donald.” “Nancy Pelosi has been doing this for quite a while, Putin has been doing this for a quite a while, Xi has been doing this quite a while. They’ve all been running circles around him.”

“The next question is when does he really realize that for what it is, and I think the answer for that is he never will,” Mr. O’Brien said, “because it would admit either defeat or acknowledgment of his inadequacies, and he will just never do that.”