Mark Sanford, the former South Carolina governor and congressman, has decided to launch a long-shot Republican challenge to Donald Trump for the presidency in 2020.

“I am here to tell you now that I am going to get in,” Sanford said in an interview on Fox News Sunday.

Sanford, 59, and Trump are longstanding political foes. When asked why he was taking on an incumbent who is popular within the party, Sanford said: “I think we need to have a conversation on what it means to be a Republican. I think that as the Republican party, we have lost our way.”

Sanford frequently questioned Trump’s motivations and qualifications during the run-up to the 2016 presidential election and called Trump’s candidacy “a particularly tough pill to swallow”.

In 2018, Trump launched an unusual attack against a then sitting House Republican only hours before polls closed in a primary election where Sanford was being challenged. He made reference to an infamous incident when Sanford disappeared while having an affair during his time serving as governor. Trump – at the time flying back from Singapore on Air Force One – attacked Sanford, urging voters to support his rival, Katie Arrington. Sanford lost the primary to Arrington.

In his tweet at that time, Trump said: “Mark Sanford has been very unhelpful to me in my campaign to Maga [Trump’s campaign slogan “make America great again”]. He is MIA [missing in action] and nothing but trouble. He is better off in Argentina. I fully endorse Katie Arrington for Congress in SC, a state I love. She is tough on crime and will continue our fight to lower taxes. VOTE Katie!”

The reference to Argentina stems from an extramarital affair that the libertarian Republican had in 2009 while serving as governor. Sanford, who was married, fell in love with an Argentinian woman, María Belén Chapur, and went to visit her after telling his staff that he would be “hiking the Appalachian trail”. He later described Chapur as his soulmate.

On Sunday morning, Sanford said he would formally announce his 2020 presidential election bid at an event in South Carolina this week.

Sanford’s announcement came when the Fox News Sunday host Chris Wallace asked him whether he had decided to run for president after expressing interest this summer.

“Are you going to enter the race against Donald Trump?” Wallace asked.

Sanford did not hesitate.

He said: “I have, and I planned to announce that back home this week. We had a hurricane come visit us on the coast of South Carolina so that sort of disrupted plans on that front, but I’m here to tell you now that I am going to get in.”

Wallace sought definitive clarity.

“You’re going to run for president against Donald Trump in the Republican race?” Wallace said.

“I am, I am,” Sanford said.

Wallace then asked Sanford why he was running. Sanford replied: “I think we need to have a conversation on what it means to be a Republican.”

Sanford later said: “We have lost our way on debt and deficits and spending. The president has called himself the king of debt.” He said that Trump’s attitude toward debt, “I think, is ultimately leading us into the wrong direction”.

Wallace responded: “You’ve got to know you basically have no chance of winning the Republican nomination. So why run for president?”

Sanford said: “I think you probably would have said that same thing to Donald Trump just a matter of months ago if he faced the likes of Jeb Bush and others.”