Former Massachusetts Gov. Bill Weld on Monday formally declared his candidacy for White House, setting him off on an extreme uphill climb to defeat incumbent President Donald Trump for the Republican nomination.

“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," said Weld in a statement as he launched his bid to try and topple Trump, who remains very popular with Republicans.

Weld, a very vocal Trump critic, also released a three-minute-long video highlighting his achievements during his two terms as governor of Massachusetts in the 1990s.

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The video also showcased clips of some of Trump’s most controversial moments, from the infamous “Access Hollywood” video of Trump using lewd language to boast of his sexual groping and kissing of women without their consent, to the president’s comments in the wake of the violence in Charlottesville, Va., where he said “there were very fine people on both sides” of the clashes between supporters and protesters of the city’s Confederate monuments.

Weld, who recently returned to the Republican Party after serving as the 2016 Libertarian Party nominee, launched a presidential exploratory committee in February.

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At that announcement, as he headlined the “Politics and Eggs” speaking series in New Hampshire, he called Trump “compulsive” and “irrational” and argued that “we have a president whose priorities are skewed toward promoting of himself rather than toward the good of the country.”

He also lamented the state of the GOP, arguing “the president has captured the Republican Party in Washington. Sad. But even sadder is that many Republicans exhibit all the symptoms of Stockholm Syndrome, identifying with their captor.”

After his announcement, Weld visited the first-in-the-nation presidential primary state numerous times. He's set to return Tuesday for a two-day swing in through New Hampshire.

Former Ohio Gov. John Kasich, another vocal Trump critic, has been mulling a GOP primary challenge against Trump. So has Maryland Gov. Larry Hogan, who heads to New Hampshire next week to headline “Politics and Eggs,” which is a must-stop for White House hopefuls.

The president's re-election campaign adviser and daughter-in-law, Lara Trump, said the president’s 2020 team hasn’t been worried at all about a Republican primary challenge.

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“I don’t know why someone would be dumb enough to challenge Donald Trump,” she told Fox News recently when asked about Weld.

“I don’t know why anybody would waste their time and money on the Republican end trying to challenge the president. We’re not worried about that at all,” added Trump, who was interviewed before headlining the New Hampshire GOP’s annual fundraising gala.