Two of President Donald Trump's Republican primary challengers made it clear Tuesday night: The 2020 presidential race isn't about electing someone else. It's about not electing Trump.

Both former Rep. Joe Walsh of Illinois and former Gov. Bill Weld of Massachusetts came out in strong support of Trump's impeachment during Business Insider's 2020 GOP debate.

They also slammed Trump on key issues including his trade war with China and climate change.

"We have begun to see in the last two months, him coming unglued, and it's time for him to be removed — that's what's going to save us all," Weld said. "It's not going to be Donald Trump. It's going to be the absence of Donald Trump."

Walsh struck a more urgent tone: "We have to do better than a president who tweets ugly insults every morning at the American people. We have to do better than a president who lies to us every time he opens his mouth. We've got to do better than a president who has zero respect for the rule of law."

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Two of President Donald Trump's Republican primary challengers set the tone right out of the gate on Tuesday evening: The 2020 race isn't about electing someone else; it's about not electing Trump.

Former Rep. Joe Walsh of Illinois and former Gov. Bill Weld of Massachusetts took the stage at Business Insider's GOP primary debate, where both argued that Trump was a threat to national security and American values and deserved to be removed from office.

"This is about Trump," Walsh said. "This is about that guy in the White House. I'm not debating Bill Weld. I've got all the respect in the world for Bill Weld."

He added: "It's not about issues — it's about Trump."

The president "deserves to be impeached and everybody should keep their boots on top of" Republicans in Congress "so that they follow their constitutional duty," Walsh said.

Weld struck a similar chord.

"We simply can't sit still for this guy, who's a disgrace to this office," he said, adding that Trump engaged in "some combination of treason, bribery, and high crimes and misdemeanors."

It's not the first time Weld has accused the president of treason. Earlier this week, he said Trump's push for Ukraine to investigate former Vice President Joe Biden ahead of the 2020 election constituted treason and specifically noted that the crime carried the death penalty.

He backed off from repeating that during Tuesday night's debate but pointed out that his time in office during the Watergate presidential scandal in the 1970s contributed to his support for Trump's impeachment.

The president declined an invitation to participate in the debate, as did another of his GOP challengers, former Gov. Mark Sanford of South Carolina, who cited a scheduling conflict.

Read more: Trump aides were so afraid he'd pressure Ukraine to investigate Biden that they tried to derail his call with the Ukrainian president

Walsh: Republican 'party bosses' are a 'cult'

Tuesday's debate came just hours after House Speaker Nancy Pelosi announced that the House of Representatives would launch a formal impeachment inquiry into Trump following revelations that he pressed Ukrainian President Volodymyr Zelensky in a July 25 phone call to investigate Biden and Biden's son Hunter over their dealings in Ukraine.

The call is believed to be at the center of an unprecedented whistleblower complaint that a member of US intelligence filed against Trump in August.

Michael Atkinson, the intelligence community inspector general, determined after a preliminary review that the complaint was "credible" and "urgent," which should have triggered a federal statute requiring the Office of the Director of National Intelligence to turn the complaint over to congressional intelligence committees.

But the acting director of national intelligence, Joseph Maguire, overruled Atkinson after consulting with the Justice Department and determined that the complaint did not meet the definition of "urgent concern" under the law because it related to a person outside the purview of the director of national intelligence. The decision was backed by the White House counsel, Pat Cipollone.

But the tide shifted after Pelosi announced the impeachment inquiry against Trump on Tuesday. Politico reported afterward that the White House was preparing to release the complaint to Congress by the end of the week. Trump also announced earlier Tuesday that he would release a transcript of his phone call with Zelensky.

Weld said Trump's conduct constituted removal from office. "You have the sitting president of the United States essentially selling the results of the presidential election in which he's the candidate," he said.

Walsh, meanwhile, said he was more taken aback by congressional Republicans who "claim that they believe in the rule of law" and "limited government." He went on to call the "party bosses" a "cult."

"They've abandoned everything they believe in to worship this guy every single day," he said.

No Republican member of Congress publicly supports impeaching Trump. Rep. Justin Amash of Michigan used to identify as a Republican but switched his affiliation to independent after facing swift backlash from GOP lawmakers for supporting an impeachment inquiry.

Read more: Trump tried to negotiate with Pelosi on the whistleblower complaint after she announced an impeachment inquiry. Pelosi told him to take a hike.

Walsh and Weld split with Trump on trade and climate change

Trump's Republican primary opponents also slammed Trump on other key issues like his trade war with China and his stance on climate change.

"Mr. Trump thinks that when he slaps a tariff on China, it's paid by China back in Beijing," Weld said. "It's not — it's paid for by American farmers or American businesses or individuals who need to import something from China that contains steel or aluminum, and everyone knows it."

Walsh echoed that criticism, blasting Trump's erratic economic policy as damaging to the nation's economy.

"The uncertainty, the hour-by-hour 'where is this president going?' has everybody in the business community on edge," Walsh said. "They're not investing, they're not hiring. This is where your slowdown is coming from."

On climate change, both Walsh and Weld argued that the GOP needed to take the threat more seriously.

"This is the issue that concerns most young Americans," Walsh said. "Republicans have to acknowledge that it's real."

Weld, who calls himself an environmentalist and favors government regulations to protect the environment, spoke in favor of one such solution in the form of a carbon tax on emissions, which he argued would incentivize businesses to cut their emissions.

The former lawmakers also zeroed in on Trump's immigration policies and said that while illegal immigration was a serious and sustained problem in the US, it should be addressed humanely and without crossing legal boundaries, as the Trump administration has been accused of doing.

They also took aim at Trump's treatment of the independent press.

"He doesn't respect the First Amendment," Walsh said. "He doesn't know what the First Amendment is. Dictators speak that way."

Weld largely agreed.

"When the president said a free press is the enemy of the people, that's straight out of the handbook, or the playbook, of Benito Mussolini and Adolf Hitler," he said. "It sent a chill down my spine."

Read more: In rare bipartisan moment, Senate unanimously votes for Trump to release whistleblower complaint to intelligence committees

Both men drilled down on tearing into Trump in their closing statements as well.

"We have begun to see in the last two months, him coming unglued, and it's time for him to be removed — that's what's going to save us all," Weld said. "It's not going to be Donald Trump. It's going to be the absence of Donald Trump."

Though Trump has maintained strong support among his base and impeachment is still thought to be unpopular among the general American public, Weld expressed doubts about Trump's chances in the 2020 election.

He said the timing of Democrats' impeachment inquiry meant the president would be inundated with unflattering headlines entering the most critical time in the campaign. "That's going to be hard to disregard, because it's going to be on page one of all the newspapers," Weld said.

Walsh struck a more urgent tone.

"I helped create Trump, period," he said, adding that Trump "hasn't done squat" for Republicans who voted for him.

"Donald Trump said he was going to drain the swamp — he is the swamp," Walsh said. "We have to do better than a president who tweets ugly insults every morning at the American people. We have to do better than a president who lies to us every time he opens his mouth. We've got to do better than a president who has zero respect for the rule of law."

Grace Panetta and Joseph Zeballos-Roig contributed to this report.