“I think we need to have a conversation on what it means to be a Republican,” he said. “As a Republican Party, we have lost our way.”
Sanford said he is saving his formal campaign announcement until after his state recovers from Hurricane Dorian.
The 59-year-old politician has been teasing a presidential run since at least the summer, when he told the Charleston Post and Courier that he thought he could be the one to focus on curtailing government spending.
A frequent critic of the president, Sanford lost his primary congressional race last year to Katie Arrington, who Trump endorsed hours before polls closed. She eventually lost in the general election to Democrat Joe Cunningham.
Sanford joins former Illinois Congressman Joe Walsh and Bill Weld, the former Massachusetts governor, as primary challengers for Trump.