Former Massachusetts Gov. Bill Weld announced Monday he was officially running for president on the GOP line — making him the first Republican to challenge President Donald Trump in the 2020 primaries.

"America deserves better," Weld's campaign announcement video said, before showing video clips of Trump mocking John McCain, imitating a disabled reporter, praising Wikileaks and the notorious "Access Hollywood" tape where he was caught on audio making inappropriate comments about women.

"It is time for patriotic men and women across our great nation to stand and plant a flag. It is time to return to the principles of Lincoln — equality, dignity, and opportunity for all. There is no greater cause on earth than to preserve what truly makes America great. I am ready to lead that fight," Weld said in a statement.

He "believes that we must preserve the democratic institutions of our Republic: the rule of law, a free and open press, and America's global leadership in maintaining a freer, safer world," his campaign said.

The announcement video noted that Weld was appointed a U.S. attorney by then-President Ronald Reagan, and that he successfully battled tough odds when he was elected as a Republican governor in a heavily Democratic state. The Harvard Law School graduate served two terms as governor of Massachusetts.

Weld, 73, has run on a ticket against Trump before — he was the Libertarian Party's vice presidential nominee in 2016, when former New Mexico Gov. Gary Johnson led the party's ticket. They got just more than 3 percent of the vote.

He changed his registration back to the GOP after the election, and announced he was forming an exploratory committee in New Hampshire in February.

"I'm here because I think our country is in grave peril," he said then. "I cannot sit quietly on the sidelines any longer."

The Trump campaign had no comment and referred reporters to a statement from the Republican National Committee.

"President Trump enjoys unprecedented support among Republicans. He has already delivered a long list of incredible accomplishments for conservatives and the country," an RNC spokesperson said. "The RNC and the Republican Party are firmly behind the president. Any effort to challenge the president’s nomination is bound to go absolutely nowhere."