It has to go through Pennsylvania, which is necessary but not sufficient.
He needs to take Pennsylvania, hold onto Georgia and North Carolina, then take either Arizona (for 279 electoral votes) or Nevada (for 274). Biden leads in both of those states. But Trump is gaining in Arizona, and it’s entirely conceivable that he could overtake Biden there (despite Fox and AP prematurely calling it for Biden).
The problem is Pennsylvania, where Trump has been losing ground fast, and Georgia, where he is hanging on by a thread. If he hangs on in Pennsylvania and wins Arizona, but drops Georgia, Biden still wins with 275 electoral votes.
The wildest scenario would be Trump holding on to Pennsylvania, falling short in Georgia, and then catching Biden in Arizona and Nevada for a 269-269 tie.
Regardless, nothing good happens for him without somehow preserving his lead in Pennsylvania.