Former Vice President Mike Pence introduced his presidential marketing campaign in Iowa on Wednesday with a repudiation of Donald J. Trump, portraying his former boss — and now rival — as unfit for the presidency and going additional than ever earlier than in condemning the character and values of the person he loyally served for 4 years.

Before a crowd of a number of hundred on the campus of the Des Moines Area Community College, Mr. Pence targeted on one thing that many in his occasion have tried to desperately keep away from: Mr. Trump’s actions on Jan. 6, 2021.

“Jan. 6 was a tragic day in the life of our nation,” Mr. Pence stated. “But thanks to the courage of law enforcement, the violence was quelled, we reconvened the Congress. The very same day, President Trump’s reckless words endangered my family and everyone at the Capitol.”

He added: “But the American people deserve to know on that fateful day, President Trump also demanded I choose between him and our Constitution. Now voters will be faced with the same choice. I chose the Constitution, and I always will.”

No different main Republican candidate for president has even talked about the assault on the Capitol in an announcement speech. Most elected Republicans have contorted themselves to keep away from ever speaking about that day — believing it solely alienates their voters. A rising variety of Republicans are going even additional, attempting to falsely reframe the assault on the Capitol as an inside job by the F.B.I. or by leftist teams pretending to be Trump supporters.

Instead, Mr. Pence described his personal actions that day in certifying Joseph R. Biden Jr.’s victory as a decisive second that proved his mettle, and Mr. Trump’s actions that day as disqualifying.

“The Republican Party must be the party of the Constitution of the United States,” Mr. Pence stated to applause.

“Anyone who puts themselves over the Constitution should never be president of the United States,” he stated. “And anyone who asks someone else to put them over the Constitution should never be president again.”

Mr. Pence’s use of the phrase “never” took him throughout a line he had not breached till now, at the same time as he has criticized Mr. Trump since Jan. 6. His announcement speech put him nearer to extra outspoken Republicans equivalent to former Representative Liz Cheney, who’ve described Mr. Trump as morally unfit to occupy the Oval Office.

With his remarks, Mr. Pence raised a direct query for his marketing campaign: As one of many standards for collaborating within the G.O.P. major debates, the Republican National Committee requires every candidate to signal a pledge that they may assist the occasion’s eventual nominee.

Mr. Pence has put himself within the potential place of getting to assist a candidate in Mr. Trump, the front-runner within the Republican Party, who he stated ought to “never” be president.

Despite that, solely minutes after his speech, Mr. Pence promised in an interview with Fox News that he would assist the Republican nominee for president, “especially if it’s me.”

The former vp addressed a thorny problem of his long-shot candidacy: learn how to account for his years of supporting a candidate whose character and positions have been well-known in 2016, and whose presidency was in line with a few of these expectations. In Mr. Pence’s telling, the Mr. Trump with whom he shared a ticket has, in truth, modified.

Mr. Pence homed in on three points to attract an ideological distinction with Mr. Trump: abortion, fiscal conservatism and overseas coverage.

“When Donald Trump ran for president in 2016, he promised to govern as a conservative. And together we did just that,” Mr. Pence stated, leaving unmentioned the inconvenient proven fact that the Trump-Pence administration added round $8 trillion to the nationwide debt.

“Today he makes no such promise,” he added. “After leading the most pro-life administration in American history, Donald Trump and others in this race are retreating from the cause of the unborn.”

While Mr. Pence went after Mr. Trump in his speech, he used an announcement video earlier within the day to assault President Biden. “Our country’s in a lot of trouble,” Mr. Pence stated in his practically three-minute-long announcement video, accusing Mr. Biden and the “radical left” of weakening America “at home and abroad.”

Citing “runaway inflation,” a looming recession, a southern border “under siege,” unchecked “enemies of freedom” in Russia, China “on the march,” and what he calls an unprecedented assault on “timeless American values,” he promised to ship what he stated the nation sorely wanted.

“We’re better than this,” Mr. Pence says. “We can turn this country around. But different times call for different leadership. Today our party and our country need a leader that’ll appeal, as Lincoln said, to the better angels of our nature.”

In his speech, Mr. Pence went on to clarify that in contrast to different Republican candidates he wouldn’t be afraid to chop spending on Social Security and Medicare as a way to confront the nation’s debt disaster.

Then he turned to overseas coverage. He stated Mr. Trump had walked away from America’s conventional position on the world stage. He described the United States as “the leader of the free world” and an “arsenal of democracy.” He criticized Mr. Trump for describing President Vladimir V. Putin of Russia as a “genius” and Gov. Ron DeSantis of Florida for describing Russia’s invasion of Ukraine as a “territorial dispute.”