WASHINGTON — It started, like so many things do in the age of Trump, with a morning tweet.

The president of the United States took to Twitter on Monday to tout all that he had accomplished in his first 500 days in office, “many believe more than any president in his first 500 days,” he tweeted.

Before long, many of those believers felt compelled to publicly agree, and, as it happened, many of them were from inside President Trump’s own administration. Cabinet secretaries and federal agencies from across the government flooded social media with messages congratulating Mr. Trump on his milestone and his accomplishments, some thanking the president personally and noting, they said, that he had delivered on his promises.

“Today marks @POTUS’ 500th Day in office, and just as he promised, the border wall has begun construction,” the official Department of Homeland Security Twitter account said in a posting that was soon recirculated by the White House. “After 500 days in office, U.S. leadership is back on the world stage as the result of @POTUS’s policies,” the State Department proclaimed.

“From ensuring clean air and water to reducing burdensome regulations, EPA celebrates @POTUS President Trump’s 500th day in office,” the Environmental Protection Agency declared, adopting the White House phrase on the occasion: “500 Days of American Greatness.” Scott Pruitt, the agency’s administrator who has been mired in scandals but is a personal favorite of Mr. Trump’s, posted a 500-day news release from his official account that concluded: “THANK YOU PRESIDENT TRUMP!” underneath an aerial photograph of the president in the Rose Garden.