Former Rep. Mark Sanford, R-S.C., said on Sunday that he will run for president, giving President Donald Trump another longshot primary challenger.

"I plan to announce that back home this week.," Sanford told "Fox News Sunday" host Chris Wallace, adding, "But I am here to tell you now that I am going to get in."

Sanford is the third Republican to announce a primary challenge to Trump, joining former Rep. Joe Walsh, R-Ill., and former Massachusetts Gov. Bill Weld. Sanford, who had for months been hinting at a presidential bid, said he is going to run "because I think we need to have a conversation on what it means to be a Republican."

"I think that as a Republican Party, we have lost our way," he continued. "And I'd say so on a couple of different fronts, I'd say first and sort of the epicenter of where I'm coming from is that we have lost our way on debt and deficits and spending."

Sanford faces an uphill battle against Trump, who enjoys widespread support among Republican voters. After Wallace pointed out that the former congressman has "basically" no shot, Sanford said the same could've been said for Trump ahead of 2016, adding "you never know" what could happen.

"I'm listing my goals, my primary goal is to say let's go out and force or try and create a conversation on that which is not being talked about in this presidential cycle," Sanford added.

Sanford served as a congressman for South Carolina's 1st Congressional District from 1995-2001 and again from 2013-2019. He served as the state's governor from 2003-2011, where he faced scandal over an extramarital affair. Sanford said he was hiking the Appalachian Trail while, in actuality, he was in Argentina with a mistress.

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Sanford lost a 2018 reelection bid to his congressional seat after Trump endorsed South Carolina state Rep. Katie Arrington, who won the primary before losing the race to now-Rep. Joe Cunningham, D-S.C. Sanford and Trump have a history of trading barbs.

"Can you believe it? I’m at 94% approval in the Republican Party, and have Three Stooges running against me," Trump tweeted last month. "One is 'Mr. Appalachian Trail' who was actually in Argentina for bad reasons. Another is a one-time BAD Congressman from Illinois who lost in his second term by a landslide, then failed in radio. The third is a man who couldn’t stand up straight while receiving an award. I should be able to take them!"

Addressing his affair, Sanford said he "learned a level of humility, a level of empathy that I didn't have before, a level of judgment" in its aftermath.

"It is something of great regret," he said. "It is something I've apologized extensively for. And in contrast to the president where he says there's not a single thing that he sort of regrets or apologizes for, I profoundly apologize for that. And I believe in the Christian model of repentance and renewal and a second chance."

"And what's been interesting in the wake of all of that, this is 10 years ago, is that subsequent of that, the folks who knew me best back home said, look, we don't approve of that chapter of life or how you handled it, but we're going to give you a second chance and we're going to send you to Congress to represent us, which I did for the following six years," he continued.

Sanford's announcement comes as his home state's GOP canceled its 2020 primary following other states canceling their Republican primaries.

"I think we need to have a conversation on the degree to which institutions and political culture are being damaged by this president," Sanford said, adding, "Those institutions and that political culture [are] really the glue that holds together our balance of power. That's a longer conversation. And finally, I think we need to have a conversation on humility and one's approach to politics. At the end of the day, a tweet is interesting, it may be newsworthy, but it's not leadership. And we're not going to solve some of the profound problems that we have as Americans by tweet."

Republicans "haven't had a choice" on Trump, Sanford said.

"And that's why I'm running," he continued. "I think that Americans deserve and need a choice."