Former Massachusetts Gov. Bill Weld announced Monday he is officially challening U.S. President Donald Trump for the Republican nomination for president in 2020.

“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,” Weld, who had previously formed an exploratory committee, said in a statement.

The former Republican governor and 2016 Libertarian nominee for vice president is exploring a primary contest against Trump.

Weld had previously said Trump will likely belittle him if he officially challenges the president.

Bill Weld on why he is exploring a Republican challenge to Trump in 2020

Weld says, “I’m not going to sit there and be a punching bag.”

Weld told the New Yorker in early March he has a strategy to beat Trump for the Republican nomination, starting with winning New Hampshire, a state where he is well-known and well-liked from his time as governor of neighboring Massachusetts.

Weld explains, "Well, if you show strength in New Hampshire, then the Trump campaign operation has to take you seriously. And I’m confident of doing well there. I think that all the New England states could be in play, the mid-Atlantic states, certainly, California, Oregon, Washington, the states in the West, the intermountain west."

Weld is a longtime critic of Trump and called the president's repeated attacks on former U.S. Senator John McCain a "national embarassment." Trump's “continued attacks on John McCain are contemptible and beneath the dignity of our American democracy,” tweeted Weld in mid-March.

Weld, who served as governor of Massachusetts from 1991 to 1997, added that “While @realDonaldTrump’s senseless attacks on allies have become all too common, his defamation of a deceased American hero has reached a new low and raises serious concerns about his mental stability and moral integrity.”