Screenshot/Fox

Add former South Carolina Gov. Mark Sanford (R) to the list.

Sanford announced Sunday that he will challenge President Trump in the Republican primaries, joining former Rep. Joe Walsh (R-Ill.) and former Massachusetts Gov. Bill Weld (R) in doing so. "I'm here to tell you now that I am going to get in," he told Chris Wallace on Fox News Sunday. "As a Republican Party, we have lost our way."

Sanford was long-rumored to launch a presidential campaign, which is likely to remain a long shot. Sanford will seemingly emphasize the increasing national debt and the need to cut back on deficit spending, though he also said he believes the country needs "to have a conversation about humility," indicating there will be a cultural aspect to the campaign, as well.

Sanford is not without his own past controversies, however — in 2009, while serving as governor, he disappeared for nearly a week, eventually admitting he was in Argentina having an extramarital affair. When asked about it by Wallace, Sanford explained he "profoundly apologized for that," which he said sets him apart from Trump. Read more at The Hill and Fox News.