Bill Weld acknowledges that he’s the longest of long-shot candidates as he prepares to challenge President Trump for the GOP primary nod.

But the former two-term Massachusetts governor points to another one-time GOP long shot who twice won New Hampshire’s first-in-the-nation presidential primary – the late Sen John McCain, R-Ariz.

WELD MAKES IT OFFICIAL, LAUNCHING A LONGSHOT PRIMARY CHALLENGE AGAINST TRUMP

In an interview with Fox News on Tuesday – the day after he formally launched his campaign to be the GOP's 2020 standard bearer – Weld pointed to McCain’s tireless style of politics, which fueled his primary victories in New Hampshire in 2000 and again in 2008, when he captured the nomination.

“John McCain made that work here twice. Not once but twice. He was the underdog both times,” Weld pointed out.

Weld – he's so far the lone GOP politician to announce a primary challenge to Trump's re-election campaign -- faces a sharp uphill climb to defeat the president, who remains popular with Republican voters in New Hampshire and across the country.

Still, Weld said he can beat Trump, emphasizing that he’s used to being the underdog, as he was in his state's gubernatorial election some 30 years back.

“When I ran for governor of Massachusetts, I was less than an asterisk,” Weld said. “And I went out to every event all summer long and into the fall and I was often all by myself. And little by little, people said, ‘This kid keeps showing up.’ And the same thing would be the plan here” in New Hampshire

Minutes before he sat down with Fox News, Weld was implementing his plan, going table to table to talk with voters at Manchester’s Airport Diner, seen by many as a must-stop for White House hopefuls. He had just come from the fabled Red Arrow Diner in downtown Manchester, his first stop in a two-day swing through the Granite State.

TRUMP'S UNPRECEDENTED 2020 CAMPAIGN WAR CHEST

Weld was in New Hampshire just two days after Trump’s re-election campaign announced it had raised $30 million in the first three months of this year -- it now boasts a war chest of more than $40 million.

Asked how he can compete, Weld said that “my calls have been going well. I’m been making some finance calls. I’m calling some people who were supporters of Mitt Romney, people who were supporters of Jeb Bush, and they’re supportive.”

He added, “I don’t think New Hampshire is a primary you can buy.”

Weld has made visits to the state almost every week since announcing in February that he was setting up a presidential exploratory committee. And he said that’ll continue.

“I could be in New Hampshire all day, every day and still sleep in my own bed in Massachusetts every night,” he said.

Independents – some 40 percent of the state’s electorate – are allowed to vote in either the Democratic or Republican presidential primaries, which could help Weld as he tries to pull the ultimate upset in the GOP nomination race.

“I’ll probably be here part of every week between now and next February,” he said. But Weld also insisted that his message could also resonate on the West Coast and in some of the Rocky Mountain states.

Weld, who’s been a very vocal critic of the president, told Fox News: “I think I can do a better job than he can. I can cut spending. I have the political will to do it. I did that in Massachusetts. ... Mr. Trump, whatever his other virtues might, he is not an economic conservative.”

What's more, Weld said he "wouldn’t turn my back on climate change and global warming the way Mr. Trump has. ... The Republican Party should not put its head in the sand on climate change.”

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.

“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.”

Weld also isn’t making any friends with the New Hampshire GOP.

State party chairman Steve Stepanek points to Weld’s insistence that he wouldn’t support Trump in the 2020 election, and to Weld’s time in 2016 as the Libertarian Party vice presidential nominee (Weld re-registered as a Republican earlier this year), and asked, “How can he call himself a Republican.”

But Stepanek – he was New Hampshire co-chairman of Trump’s 2016 campaign -- said Weld would get a fair shake, adding that “essentially I am neutral in the primary as far as Governor Weld is concerned.”

Former Ohio Gov. John Kasich, another vocal Trump critic, has also 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,” another important event for White House hopefuls.

“I spoke to both of them in the last few days. Very pleasant conversations,” Weld shared.

Asked if he would exit the race if either Kasich or Hogan jumped in, he quickly answered: “I wouldn’t get out. I’d compete, but it would be an honorable competition.”

He said multiple primary challengers “could be good for President Trump, sharpening him up a little bit so that he wouldn’t take everything for granted. ... It might be harder for President Trump to duck debates if there were three other candidates here."