Former US vice president Mike Pence opened his bid for the Republican nomination for president on Wednesday with a firm denunciation of former president Donald Trump, accusing his two-time running mate of abandoning conservative principles and being guilty of dereliction of duty on January 6 2021.

Mr Pence, launching his campaign in a suburb of Des Moines, Iowa, became the first vice president in modern history to challenge the president under whom he served.

He said Mr Trump had disqualified himself when he insisted that Mr Pence had the power to keep him in office — even though he did not.

Mr Trump, he said, “endangered my family and everyone at the Capitol” on January 6. “But the American people deserve to know that on that day, president Trump also demanded I choose between him and our Constitution. Now voters will be faced with the same choice.”

“I believe anyone that 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,” he said.

Pence has spent much of the past two-and-a-half-years obliquely criticising Mr Trump, trying to navigate his political future in a party that has been transformed in Trump’s image.

But on Wednesday, as he made his pitch to voters for the first time as a declared candidate, he did not hold his tongue.

He accused the former president of abandoning the conservative values he ran on, including on abortion.

Mr Pence, who supports a national ban on the procedure said: “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.

“The sanctity of life has been our party’s calling for half a century – long before Donald Trump was a part of it. Now he treats it as an inconvenience, even blaming our election losses in 2022 on overturning Roe v Wade.”

Mr Trump has declined to say what limits he supports nationally and has blamed some midterm candidates’ rhetoric for their losses last November.

Mr Pence also bemoaned the current politics of “grudges and grievances”, saying the country needs leaders who know the difference between the “politics of outrage and standing firm”.

“We will restore a threshold of civility in public life,” he pledged.

With Pence’s entry into the race, on his 64th birthday, the GOP field is largely set.

It includes Mr Trump, who’s leading in early polls, Florida governor Ron DeSantis, who remains in second, former United Nations Ambassador Nikki Haley, South Carolina senator Tim Scott, former New Jersey governor Chris Christie, former Arkansas governor Asa Hutchinson and North Dakota governor Doug Burgum, who also launched his campaign on Wednesday.

Mr Pence’s campaign will test the party’s appetite for a socially conservative, mild-mannered and deeply religious candidate who has criticised the populist tide that has swept through his party under Mr Trump.

And it will show whether Mr Pence has a political future when many in his party still believe Mr Trump’s false statements that the 2020 election was stolen and that Mr Pence had the power to reject the results of the election, won by Democrat Joe Biden.