Trump's strategy is pretty basic - divide and conquer. The more contenders for the nomination, the more they'll split the anti-Trump vote. So Scott entering probably probably makes Trump him happy.
The only way that doesn't work is if one contender gets a quick jump that convinces the others to drop out. So the way he prevents that is by focusing everything on whomever is on the lead. In this case, that's DeSantis. And if he were to drop out, Trump would then turn on whomever is second and leave the rest alone. And so on. If it works, he'll be the nominee.
He then figures that when everyone else is gone, and regardless of what else he has said and done, GOP voters will overwhelmingly rally around him again.
I think he's going to be surprised.