Libertarian candidate for Vice President and former Massachusetts governor Bill Weld speaks to students in Boston, Mass. in 2016.

However, Trump retains high popularity among Republicans, which, if sustained, will make it very difficult for any challenger to defeat him in a contest for the GOP nomination.

New Hampshire holds the first primary of the 2020 nomination contest, and has long been seen favorable campaigning grounds for both Republicans and Democrats from neighboring Massachusetts.

Weld, 73, plans to be in New Hampshire on Tuesday for the first of two days of campaigning.

"I'm in!" Weld said in a tweet announcing his candidacy, the first so far by a GOP contender to try to deny Trump's bid for a second term in the White House.

William Weld, the former two-term governor of Massachusetts, announced Monday that he will challenge President Donald Trump for the Republican nomination for president in 2020.

Weld, a former United States Attorney appointed by President Ronald Reagan, later served as the Republican governor of Massachusetts from 1991 to 1997.

Weld was the Libertarian Party's nominee for vice president in 2016 on a ticket headed by ex-New Mexico governor Gary Johnson. He and Johnson won nearly 4.9 million votes, or 3.28 percent of the popular ballots cast, finishing well behind Trump, who won 46 percent of the popular vote, and Democratic nominee Hillary Clinton, who finished first in the popular balloting with 48.18 percent. Trump won the presidency by getting 304 votes in the Electoral College.

In a statement, Weld described his intention to return the United States "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.

His campaign web site touted his having as governor "cut taxes 21 times, never raised them, balanced the budget, and oversaw six upgrades in the state's bond rating."

"He signed landmark welfare reform, established public education standards, and was a trailblazer as an early proponent for LGBT civil rights," the site said.

But a spokesman for the Republican National Committee was dismissive of Weld's challenge, noting, "President Trump enjoys unprecedented support among Republicans."

"He has already delivered a long list of incredible accomplishments for conservatives and the country. The RNC and the Republican Party are firmly behind the president," the spokesman said.

"Any effort to challenge the president's nomination is bound to go absolutely nowhere."

Weld's campaign web site, www.weld2020.org, posted a three-minute video that opens up with the words, "America Has a Choice."

"New Hampshire, 2019," a voice says on the video. "A better America starts here. Bill Weld for president. Join us."

Weld said, "Ours is a nation built on courage, resilience, and independence. In these times of great political strife, when both major parties are entrenched in their 'win at all cost' battles, the voices of the American people are being ignored and our nation is suffering."

"It is time for patriotic men and women across our great nation to stand and plant a flag," he said.

On the video, Weld touts his conservative principles and successes as the first Republican governor of Massachusetts in more than a decade.

He depicts a corroded Democrat-led political machine that leaned heavily on tax increases and welfare programs, and casts himself as its libertarian antithesis.

Declaring that "America deserves better," the video then shifts to Trump, targeting some of the president's most controversial remarks.

It includes clips of Trump dismissing the late Arizona Sen. John McCain's service in the Vietnam War and appearing to mockingly mimic a disabled reporter. It also has audio of Trump, on the infamous "Access Hollywood" tape, boasting about groping women without their consent.