Sanford said the Republican Party is facing an identity crisis, and he wants the GOP to take a look at itself and do some soul searching.
"I think we have to have a conversation about what it means to be a Republican," Sanford told "Fox News Sunday," claiming the party "has lost our way."
Sanford specifically made reference to the debt, deficit and government spending. Other conservatives expressed concern about these issues when Trump helped Congress pass a spending bill that increases spending caps and suspends the debt ceiling, allowing for more government borrowing until July 31, 2021. Sen. Rand Paul, R-Ky., blasted his colleagues at the time, saying it "marks the death of the Tea Party movement in America."
Sanford also challenged Trump's tactics when it comes to trade, saying that engaging the world when it comes to trade is "one of the hallmarks of the Republican Party."
He also brought up political culture, which he said has been "damaged" by Trump.
"We need to have a conversation about humility," Sanford said, blasting Trump's social media habits by claiming that a tweet "is not leadership."
Earlier this summer, when Sanford was still deciding whether to run, he admitted, "I don’t think anybody’s going to beat Donald Trump."
When pressed on why he is running a race that he knows he will likely lose, Sanford said, "this is the beginning of a long walk, but it begins with a first step.”
Host Chris Wallace grilled Sanford on his own controversies, which include a stretch of nearly a week in 2009 during his term as governor, when he disappeared only to eventually admit that he was in Argentina having an extramarital affair. At the time, his spokesperson said Sanford was hiking the Appalachian Trail.
Sanford said he "profoundly apologized for that," contrasting his remorse with Trump, who he said does not apologize for anything. Trump poked fun at Sanford after his scandal was brought to light, but Sanford insisted that his campaign against the president was not personal.
Sanford is now the third Republican to announce a run against Trump in the primaries, with former Massachusetts Gov. Bill Weld and former Illinois Rep. Joe Walsh previously announcing their campaigns.
After Weld and Walsh stated they were running against Trump, Politico reported that the Republican parties of Arizona, Kansas, Nevada and South Carolina were looking to scrap their primaries and caucuses.
"Trump and his allies and the Republican National Committee are doing whatever they can do to eliminate primaries in certain states and make it very difficult for primary challengers to get on the ballot in a number of states,” Walsh told Politico. Weld reacted by tweeting, "Donald Trump, by turns arrogant and paranoid, has made no secret of the fact that he wishes to be crowned as president rather than elected. That might be fine in a monarchy, but we overthrew ours two centuries ago."
Kansas Republican Party Executive Director Shannon Golden, meanwhile, defended the decision, telling Fox News that the state never has Republican primaries when there is a GOP incumbent.
Fox News' Paul Steinhauser and Adam Shaw contributed to this report.