Libertarian nominee Gary Johnson and his running mate Bill Weld are bashing Republican presidential candidate Donald Trump just weeks ahead of the first debate, questioning why any member of the GOP would vote for the billionaire in a Wednesday interview with “CBS This Morning.”

When asked whether Weld -- a former Republican governor of Massachusetts -- has permanently left the Republican party, the Libertarian vice presidential nominee responded: “Yes, I have and I told the Libertarians I would never return.”

Weld added a caveat: “It doesn’t mean I’m not friendly, but it means I get to ask out loud: Why would any Republican vote for Donald Trump? He’s anti-free trade, he’s pro-entitlements, he’s terrible on the budgets, he’s unreliable.”

The Libertarian candidates also slammed Trump on his immigration policies and for parroting a “canard” that all undocumented immigrants would like a path to legal U.S. citizenship.

“There’s a reason why there are 11 million undocumented workers in this country-- it’s that it’s impossible to get across the border legally,” said Johnson, a former New Mexico governor. He later proposed to make it easier for those in the country illegally to get a work visa, “as long as they’ve been law abiding… get them in the system and out of the shadows.”

“It’s a labor force issue,” Weld added. “But Mr. Trump has planted this canard in the public consciousness that all eleven million undocumented workers are, you know, champing at the bit to become citizens. That’s just not true.”

The two also talked tax policy, including their proposals to abolish the Internal Revenue Service and instead institute a federal consumption tax.

“If I could waive a magic wand, I would eliminate income tax, I would eliminate corporate tax and replace it with one federal consumption tax,” Johnson said.

Defending the regressive nature of a consumption tax, he continued: “The way that the fair tax deals with with it being regressive, is that it issues everybody in country a prebate check of 200 dollars a month which allow everyone to pay the consumption tax up to the point of the poverty level.”

With the first presidential debate fast approaching, the Libertarian ticket also discussed their chances of garnering enough national support to earn a spot on the debate stage.

“It isn’t game over if we’re not in the first debate,” Johnson said. “But if we’re not in the debates, it is game over. I mean, there’s no way that you can win the presidential race without being in the debates.”

“If we’re in the presidential debates, 100 percent of people will know who we are and we think we have the chance to run the table,” he added, pointing to polls in states that show their voter support in double digits.

“We think we have winning arguments,” Weld said. “You know, we’re fiscally responsible, we’re socially inclusive, that doesn’t describe either of the other parties. No one would accuse the Democrats of being fiscally responsible when it comes to the budget...and the Republicans said, you know they made their platform even meaner than it was before their convention to be exclusionary towards certain groups.”