Former South Carolina governor and congressman Mark Sanford announced on "Fox News Sunday" that he is launching a primary challenge against President Trump.

"As a Republican Party, we have lost our way, and I'd say so on a couple of different fronts. 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. One of the hallmarks of the Republican Party and the conservative movement has always been how much do we spend. ... I think as a party we've lost our way. The president has called himself the king of debt, has a familiarity and comfort level with debt that I think is ultimately leading us in the wrong direction."

The big picture: Sanford, who lost his congressional primary in 2018 after Trump encouraged voters to ditch him, joins former Rep. Joe Walsh (R-Ill.) and former Gov. Bill Weld (R-Mass.) in the long-shot effort to oust Trump as the Republican nominee in 2020. Trump enjoys a near-90% approval rating in the Republican Party and is unlikely to be defeated in a primary.

Sanford is well-known for a scandal in which he disappeared for a week in 2009, telling his staff that he would be hiking on the Appalachian Trail. In reality, the then-married governor was engaged in an extramarital affair with a woman in Argentina.

Sanford addressed the controversy on Fox, telling Chris Wallace:

"I actually went on an apology tour, if you want to call it that, back home in the wake of that for the last year and a half of my governorship. And what I learned through that is, I guess what General Mattis talks about. The mistakes in life, mistakes that we make, are the great tuitions of life. They cost us, but you can learn from them. And for me, I learned a level of humility, a level of empathy that I didn't have before, a level of judgment. It is something of great regret. It's something I have apologized extensively for and in contrast to the president when he says there's not a single thing that he sort of regrets or apologizes for. I profoundly apologize for that.

Worth noting: Both Kansas and South Carolina's Republican parties shuttered their 2020 presidential primaries last week, making the long-shot GOP challengers even less likely to succeed.

This story is developing. Please check back for updates.