Washington(CNN) Former Massachusetts governor and longshot candidate for the Republican nomination for president Bill Weld levied a series of attacks against his primary opponent, President Donald Trump, dubbing him a "raging racist."

"Donald Trump is a raging racist, Okay? He's a complete and thoroughgoing racist. And he made that choice, a choice a long time ago, when he was engaged in the housing business in New York with his father," Weld said, speaking at the NAACP convention in Detroit on Wednesday.

He added: "The national Republican Party, has a choice. And a lot of them like to think that it's a political choice. But it's not a political choice. It's a moral choice."

"Unless the Republican Party in Washington expressly, expressly rejects the racism of Donald Trump, they're going to come to be universally viewed as the party of racism in America," the long-shot challenger to Trump said.

Weld's comments come a week after Trump lodged racist attacks at Democratic Reps. Alexandria Ocasio-Cortez of New York, Rashida Tlaib of Michigan, Illhan Omar of Minnesota and Ayanna Pressley of Massachusetts when he tweeted that they should "go back and help fix the totally broken and crime infested places from which they came."

The tweets were widely condemned by congressional Democrats and some Republicans, and the House passed a resolution condemning the racist language Trump used.

Weld, the former two-term Republican governor of Massachusetts, officially announced his primary challenge to Trump in April, making him the President's only Republican opponent so far in the 2020 election. In 2016, Weld was the vice presidential nominee on the Libertarian Party ticket with former New Mexico Gov. Gary Johnson.

Weld is a staunch critic of the President, telling CNN's Jake Tapper on "The Lead" in April that it would be a "political tragedy" and he would "fear for the Republic" if the country had six more years of Trump as president.

And, prodded by the release of a redacted version of special counsel Robert Mueller's investigation into Russian meddling in the 2016 election, Weld ratcheted up his rhetoric against the President, calling for his resignation.

"If Donald Trump is an American patriot, he should resign from office," Weld wrote in an op-ed published in The Bulwark, an online platform that publishes conservative commentary, in April.