WASHINGTON — Since early in his tenure, President Trump has sought to stage a military parade through the heart of Washington, only to be thwarted. So now he has settled on the next best thing: He will take over an existing patriotic display in the capital.

The Trump administration has ordered major changes in the traditional Fourth of July celebration that draws hundreds of thousands of people to the National Mall each year — with Mr. Trump personally taking a starring role as no other president has in modern times.

The mayor’s office in Washington said on Wednesday that it had been informed that Mr. Trump intended to address the assembled crowd from the steps of the Lincoln Memorial; his speech would presumably be televised to the nation. Critics said the move would transform what has for decades been a nonpartisan, unifying event into a political rally for a divisive president.

“He can’t resist injecting partisan politics into the most nonpartisan sacred American holiday there is: the Fourth of July,” said Representative Gerald E. Connolly, a Democrat from suburban Virginia who represents many of those who typically attend the Independence Day events in the capital. He called it “part of a pattern of driving wedges between Americans and making himself the subject of attention.”