Confident that there are not enough votes to remove him from office through an impeachment trial in the Senate, Mr. Trump and his advisers have chosen the path of maximum resistance, calculating that they can put the Democrats on the defensive in a fight that is politically useful for the president.

The decision to assert executive privilege and defy subpoenas across the board suits Mr. Trump’s natural combative instincts and fits the grievance narrative he has adopted by arguing that the establishment is out to get him. The president seems eager to force the hand of Democrats who are investigating him as if they are conducting an impeachment inquiry without actually calling it that and risking any of the political problems that might come with it.

“If it’s an impeachment proceeding, then somebody should call it that,” said Rudolph W. Giuliani, one of the president’s personal lawyers. “If you don’t call their bluff now, they’ll just keep slithering around for four, five, six months.”

He added, “It’s a valid strategy to test: What are you doing?”