He would scroll his own Twitter feed, looking at the replies for new topics to throw out. He studied the Twitter trending lists as signals of where the discourse was headed.

In some way, television became the medium through which he could watch the effects of his tweets.

The television in his alcove dining room off the Oval Office was usually on in the background, catnip for his short attention span. He consumed much of his information through it and watched the coverage of his tweets.

Mr. Trump’s White House aides said he loved tweeting and then watching the chyrons on cable news channels quickly change in response. For a septuagenarian whose closest allies and aides say often exhibits the emotional development of a preteen, and for whom attention has been a narcotic, the instant gratification of his tweets was hard to match.