Sanford’s chances are, of course, pretty much zero. It is almost impossible to successfully mount a primary challenge to a sitting president who has his party’s firm support. And Sanford also has his own political baggage. He had a very public extramarital affair in 2009.
So why is he doing it at all? One common guess is that he intends to use the primary as a bully pulpit to criticize Trump, even though he knows there’s no chance of actually winning.