Three Republican presidential candidates on Monday debated topics ranging from climate change to impeachment in Detroit.

While President Donald Trump did not participate, his opponents in the Republican presidential primary – former Massachusetts Gov. Bill Weld, former U.S. Rep. Joe Walsh (R-Ill.) and former U.S. Rep. Mark Sanford (R-S.C.) – were there. The event was held as part of the Forbes Under 30 Summit at the Masonic Temple.

Trump’s presence was certainly still felt at the debate.

“I wouldn’t be standing up here if Donald Trump wasn’t president,” Walsh said. “I’m concerned about the debt; I think tariffs are lousy, I can’t stand the fact that he kisses [North Korean leader] Kim Jong-Un’s feet every day. But this isn’t about the issues. This is about a guy who is a clear and present danger to this country. He’s a would-be dictator.”

For that reason, Walsh, a former Tea Party congressman, said he supports impeaching the president.

“Donald Trump’s a traitor. … If soliciting political dirt on your opponent [Joe Biden] from a foreign government [Ukraine] is not impeachable and betraying the country doesn’t demand you’re removed from office, then nothing [will],” Walsh said.

“When it comes to how impeachment might play politically, I don’t give a damn. I don’t care. This guy has betrayed this country. He’s told foreign governments to sabotage our elections. The politics of that be damned; he needs to be removed. There comes a point where politicians simply have to do the right thing, no matter how the politics are.”

Weld agreed, warning that if Trump is not impeached, Republicans may lose control of the U.S. Senate in 2020.

“If he hangs around and contests the election of 2020 and beyond and keeps fomenting civil war – his words, not mine – I think he’s going to destroy the Republican Party,” said Weld, who ran for vice president on the Libertarian ticket in 2016.

“If he succeeds in making those Republicans in the Senate walk the plank and defend him against the charges, they are all going to lose their seats, you are not going to see a Republican Senate, and I think you’re going to see the Republican Party split up and disappear.”

But Sanford disagreed, saying that the only good way to remove Trump from office is at the ballot box.

“I think what we’re setting up is validating Donald Trump’s actions,” Sanford said. “If you impeach in the House and don’t actually remove in the Senate, what it does is it allows him to say to the American public, ‘What I did was not wrong.’ … The question you have to ask is, do you want the impeachment merit badge or do you want him out of office?”

Still, Sanford would not rule out voting for Trump in 2020 if he once again wins the party’s nomination.

“The question that I have to ask is: what brings us more quickly to extinction, American debt or Donald Trump? And that’s a tough one, sadly,” Sanford said. “Trump is a temporary phenomenon, and a lot of what Bernie [Sanders] and others have proposed with $30-plus trillion in additional spending would be awfully tough.”

Weld said that he would not vote for Trump in 2020 and would instead vote for Democratic former Vice President Joe Biden if he is the nominee.

“I would never support Donald Trump for any office, ever, under any circumstances. I would certainly vote for Joe Biden over Donald Trump,” Weld said. “He’s only spending $1.6 trillion on climate change, as opposed to Sanders’ $16.3 trillion.”

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If he loses the primary, however, Weld said that he would not run a third-party campaign.

Walsh also committed to not vote for Trump in 2020, but did not rule out the possibility of launching a third-party bid if he loses the Republican primary, possibly with a Democratic running mate.

“I’m doing this because I think Trump is unfit. I think he’s a whack job. I think he’s a horrible human being. I believe, in my bones, that he is a danger to this country,” Walsh said. “And if we give him four more years, our democratic institutions are at risk. There’s no way in hell I could vote for that guy again, ever.”

The GOP candidates frequently criticized the high costs of Democratic presidential candidates’ various policies. They recognized the importance of climate change, but argued that debt is an equally concerning problem.

“There are two extinction events for all of us as Americans. One will be climate change, and the other is the American debt,” Sanford said. “I think, in particular, to remedy, what we need to do is to take a real look at nuclear energy.”

Sanford said that he would love to expand wind, solar and hydro energy, but argued that in a highly industrialized society like the United States, it “won’t get us there.”

Walsh also warned that Republicans have to recognize that climate change exists and supports a carbon tax to address the issue, saying a solution less expensive than the progressive Green New Deal is needed.

“If the Republican Party does not wake up to this issue of climate change, the Republican party will die. … We’ve got to look at free market solutions, a carbon tax,” Walsh said. “I understand it’s really appealing, these Democrats – Elizabeth Warren and the rest – saying, ‘Free this and free that.’ We have a young audience right now; we’re bankrupting you. When you’re our age, you’re going to pay back the bills for all of this free stuff.”

Weld also supports a carbon tax.

“What we need to do is put a price on carbon to reduce the amount of carbon in the atmosphere,” Weld said. “That’s our duty – it’s not to pledge $16 trillion, which is what Sen. Sanders has said. And, indeed, most of the Democratic plans dealing with climate change are defined by the number of trillions of dollars.”

Addressing climate change is just one way that the Republican candidates said they can appeal to younger voters.

Another way, Weld said, would be to allow millennials to vote on their cell phones, which Weld says are already more secure than the current system thanks to fingerprint readers.

Several states have canceled their Republican primaries in an effort to help Trump’s re-election bid. Michigan has changed its rules to give the president a better shot at winning next year.

But Sanford said that is more a sign of Trump’s weakness than a setback for the three candidates who participated in the debate.

“I think that it says, more than anything, that some within the Trump organization [are] worried. Because in the world of politics, if you have a chance to pick up an 80 or 90% — which is what they allege their support to be — and you don’t pick it up it’s because somebody’s looking at numbers, that says their support’s a mile wide, but maybe an inch deep,” Sanford said.

Weld was one of 10 presidential hopefuls — and the only Republican — who participated in the NAACP national convention forum in July in Detroit.

Twenty Democratic presidential candidates debated at the Fox Theatre across two nights in July. Ann Arbor has been selected to host one of three general election debates next year.