I think he's running to scoop up the Trump voters in the event that Trump is disqualified from running or is otherwise unavailable. If the Trumplicans are forced to abandon ship, he wants to be the obvious next choice.

But you're right about his ultimate goal. I don't believe he thinks he has a good chance to actually win the presidency. If he is the republican nominee, there are going to be an awful lot of racists staying home on election day.