Former vice president Mike Pence said Friday he will not endorse Donald Trump, the president with whom he served, just days after Trump secured the Republican Party's 2024 nomination.

Pence served under Trump but has been critical of the former president after the Jan. 6, 2021, attack on the U.S. Capitol in which Pence was targeted by a mob of pro-Trump supporters.

Pence rebuked his former boss in strong terms Friday, saying Trump's agenda doesn't align with conservatives. "Donald Trump is pursuing and articulating an agenda that is at odds with the conservative agenda that we governed on during our four years, and that is why I cannot in good conscience endorse Donald Trump in this campaign," Pence told Fox News.

The former vice president ran against Trump in the 2024 Republican primary but dropped out in October.

Pence's refusal to endorse Trump now stands out as many other former intraparty rivals and critics have consolidated behind the former president. Earlier this month, Senate Minority Leader Mitch McConnell (R-Ky.) endorsed Trump, a striking turnaround after McConnell blamed Trump for the Capitol attack three years ago.

Pence most sharply split with Trump on Jan. 6, 2021, when he refused Trump's pressure to overturn his 2020 reelection defeat. But Pence said Friday that he has "profound differences" with Trump that go beyond the events of that day, including on the national debt, abortion and China.

He told Fox News he will keep his November vote private but emphasized that he will not vote for Trump's Democratic opponent, President Joe Biden.

During his campaign announcement in June, Pence excoriated the former president for his actions during the Jan. 6 attack and his efforts to overturn his 2020 election loss. At the time, Pence declared: "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 also challenged Trump for his positions on abortion and entitlement programs, and his past comments about Russian President Vladimir Putin.

During his campaign, Pence sought to return the GOP to more Reagan-era policy priorities and warned against the "siren song of populism." Pence had said he would sign a Republican National Committee pledge to support the eventual nominee.

The former vice president dutifully served Trump for four years, until he broke with the president over certifying the 2020 election results. Trump picked Pence in 2016 to be his running mate. At the time, he was governor of Indiana.