When it comes to challenging the incumbent president in your own party, you need to be able to do a couple of things in order to even have a shot.
The first thing you need to do is have a squeaky clean past. If you think you should challenge the man who is the leader of your party, you need to make sure that at the very least your sins aren’t the same as his sins.
The second thing you need is a plan. You are trying to wrest control of your party away from someone you think is a lunatic, so you need to have some basic rough draft of a plan put together that you can present and say “This is how we’re going to do it.”
The third thing you need is at least a snowball’s chance in hell.
At no point in any of the musings, writings, or statements of Mark Sanford does he confirm that he has these three things. If he had, it would have been a lie, because he does not.
It simply would not be fair to write a column about Sanford solely making fun of his own sins, which he has apologized to the public for and sought atonement for. However, his past sins to make going after Trump significantly harder.
After all, Trump has openly bragged about his affairs and has never shied away from them. His early life story was built on his successes with women as much as it was his successes in real estate. It was something that people just expected of him, which is largely why the news of the Stormy Daniels affairs never really hurt him in any way with his supporters.
Sanford, however, carried on an affair in secret and used taxpayer money in the process of carrying his affair on. He did it to hide the affair from his family and his constituency. He spent time lying about it because he knew it was wrong and knew that people would judge him for it.
If a large part of your argument against Trump is about the respectability and decency of the office, then the above paragraph alone is probably enough to disqualify you. But that isn’t the extent of the problems Sanford will face as a primary challenger.
There is no plan for Sanford to take any noticeable votes from Trump. No path he can take to pose a threat to the president. He hasn’t offered one, and short of harnessing the votes of an alternate universe, there is no way to create one. Trump has the base firmly on his side, so Sanford can’t take any of that, and his own past makes it unlikely that other wavering Republicans would look elsewhere.
Democrats certainly won’t choose him. Independents are already trying to decide if they can go with Biden or side with Trump if an absolute trainwreck of a socialist (see: Elizabeth Warren, Bernie Sanders) gets nominated. The worst-case scenario is that they just stay home. They won’t vote for a longshot Republican challenger like Sanford.
He is also going up against a raving lunatic of a radio host who was a raving lunatic of a Trump supporter early on (Joe Walsh) and the only man I’ve ever seen in a presidential election actually have less than zero energy (Bill Weld). If these three are the best that the anti-Trump Republicans can come up with, then they are foolish and would be better served if they just left the party and went elsewhere (Britain maybe? I hear they need some new conservative voices).
If Sanford isn’t running solely to lift his name ID or sell a book, then he’s a delusional maniac. There is nothing for him on the path he’s chose to take.