Former Massachusetts Gov. Bill Weld said Sunday he would challenge President Trump on his "reckless" spending if he runs against him for the 2020 GOP nomination, while offering a broader critique of Trump's style and demeanor.

Weld emphasized fiscal conservatism as a central campaign issue days after the national debt surpassed $22 trillion, saying during a television appearance, "I'm going to make clear that I think the president is reckless in spending."

"They're spending a trillion dollars a year. They don't have that. It's going to crush Generation Xers and millennials in this country," Weld said on ABC's "This Week."

Weld formed an exploratory committee last week as he mulls a run against Trump in 2020 after recently returning to the Republican Party. Weld served as the Republican governor of Massachusetts from 1991 to 1997, before endorsing former President Barack Obama, a Democrat, in 2008. In 2016, he was the Libertarian Party's vice presidential nominee.

"He wants to divide the country and hold up, you know, scary boogeymen that everyone else can think only he can save us," Weld said of Trump. "It's part of a plan, I think, on his part to make himself seem indispensable. He's not indispensable at all."

During the interview, Weld also cast doubt on Trump's Friday declaration of a national emergency to build a southern border wall, saying people illegally crossing the border are "not a major national security threat to the United States."

Trump addressed the rising national debt Friday during a Rose Garden press conference, saying that he felt obligated to boost military spending and that a well-performing economy could increase government revenue. "Well, it's all about growth," he said.