(Bloomberg) -- Former Vice President Mike Pence kicked off his campaign challenging Donald Trump for the 2024 Republican presidential nomination with a stinging rebuke of his onetime boss, saying he should never return to the White House.

Pence, in an announcement speech on Wednesday, said Trump had abandoned conservative positions, divided the country and was wrong to ask him to violate his oath to the US Constitution and overturn the 2020 election during the Jan. 6 insurrection.

“Anyone who puts themselves over the Constitution should never be president of the United States, and anyone who asks someone else to put them over the Constitution should never be president of the United States again,” Pence said in Iowa, which has the first-in-the-nation GOP caucuses and where he’s concentrating his campaign.

The former Indiana congressman and governor, who turned 64 on Wednesday, joins a crowded and growing GOP roster with more than 10 candidates. North Dakota Governor Doug Burgum also announced his candidacy Wednesday.

Read more: Burgum Latest to Join 2024 Race: Here Are the Other Contenders

Pence said  he’ll “always be grateful for what President Trump did for this country” and was proud to stand by Trump as his vice president “every single day when we made America great again.” But Pence said addressing the problems the US faces requires new leadership in the White House and Republican Party.

Trump governed like a conservative but has since retreated from those positions, Pence said. He questioned Trump’s commitment to restricting abortion and reforming entitlement programs and the former president’s defense of Russian President Vladimir Putin.

Pence also criticized Florida Governor Ron DeSantis, currently Trump’s top rival for the GOP nomination, for calling Russia’s war with Ukraine a “territorial dispute.”

“I know we can beat Joe Biden,” Pence said. “But we must resist the politics of personality and the siren song of populism unmoored to conservative principles.” 

During a CNN town hall from Iowa on Wednesday night, Pence referred Trump’s previous comments that Putin was “a genius” and his refusal to say whether Ukraine should win the war. “I know the difference between a genius and a war criminal, and I know who needs to win,” Pence said.

As Trump’s vice president, Pence was loyal to a point critics called obsequious. A breaking point came during the Jan. 6 insurrection, when he refused Trump’s demand to reject Electoral College votes for President Joe Biden. Pence said he didn’t have the constitutional authority, prompting some in the mob that stormed the US Capitol to chant “Hang Mike Pence.”

“I stand before you today as a candidate for president to say to the Republican Party: the Republican Party must be the party of the Constitution of the United States,” Pence said in his speech.

Asked on the CNN town hall about reports that Trump’s legal team has been notified by the Justice Department that the former president is a target in a federal investigation into his handling of classified documents, Pence said he hoped his former boss would not be charged and declined to say whether he would pardon him.

“I would just hope that there would be a way for them to move forward without the dramatic and drastic and divisive step of indicting a former president of the United States,” Pence said.

But unlike Trump, who has said he would pardon people who stormed the US Capitol, Pence said he has “no interest or no intention of pardoning those that assaulted police officers, who vandalized our capital, they need to be answerable to the law.”

Despite his view that the former president is not fit for office, Pence said he would agree to support the GOP nominee if it’s not him — a requirement for participating in the GOP debates — because he doesn’t think Trump will be the nominee.

Pence is offering himself as the only traditional conservative in the field who can win the nomination, defeat Biden — and govern with more civility than Trump. 

“We know how to be good neighbors. That’s not too much to ask our leaders to do the same,” Pence said. “But sadly, it’s clear that neither Joe Biden or Donald Trump share this belief, and neither of them intend to even try to bring our country together.”

Earlier: Pence Calls for End to Fed’s Jobs Role as He Weighs 2024 Bid

In an almost three-minute campaign video released on Wednesday announcing his candidacy, Pence said that “different times call for different leadership” and the GOP and US “need a leader that’ll appeal, as Lincoln said, to the better angels of our nature.”

Pence said in the video that the US is in trouble and that Biden and “the radical left have weakened America at home and abroad.” Among the threats he said the nation faced were inflation, a looming recession and a southern US border “under siege.”

Critics question whether Pence has a viable path through the primaries, given his inability so far to win over hard-core Trump supporters who haven’t forgiven him for defying Trump and Republicans looking for an alternative. He hasn’t yet broken out of the lower tier of candidates in early polling despite his almost-universal name recognition.

“I wish him a lot of luck,” Trump said in an interview Monday with radio host Todd Starnes. “He’s a nice person. We had a very good relationship until the very end.”

Pence is promising to restore the policies of what he calls the “Trump-Pence administration” that are popular with Republican voters, while breaking from his former running mate. He’s focusing his campaign on Iowa, where he hopes to connect with evangelical voters and Iowans as a fellow Midwesterner. 

“We’re going to organize Iowa, all 99 counties, like we’re running him for county sheriff,” Scott Reed, co-chairman of the super political action committee supporting Pence, told reporters last month.

(Updates with Pence comments on CNN town hall, from ninth paragraph.)

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