Now, the president who once declared that “I alone can fix” the system increasingly stands alone in a system that seems as broken as ever. The swirl of recent days — a government shutdown, spiraling scandals, tumbling stock markets, abrupt troop withdrawals and the resignation of his alienated defense secretary — has left the impression of a presidency at risk of spinning out of control.

At the midpoint of his term, Mr. Trump has grown more sure of his own judgment and more cut off from anyone else’s than at any point since taking office. He spends ever more time in front of a television, often retreating to his residence out of concern that he is being watched too closely. As he sheds advisers at a head-spinning rate, he reaches out to old associates, complaining that few of the people around him were there at the beginning.

Mr. Trump is said by advisers to be consumed by the multiplying investigations that have taken down his personal lawyer, campaign chairman, national security adviser and family foundation. He rails against enemies, who often were once friends, nursing a deep sense of betrayal and grievance as they turn on him.

“Can you believe this?” he has said as he scanned the torrent of headlines. “I’m doing great, but it’s a war every day.”