Nay, in reality that would be political suicide. Then again, this ain't the real world anymore...
Trump only cares about the MAGAs. Why in the world wouldn't he pardon him?
Pardoning a domestic terrorist would mean losing all support from independents and all Republican support outside his base. 2020 would be a rout.
He's a political zombie.
Anyhow, they can charge the guy with state crimes, which can't be pardoned.
... and the FBI identified and found him, based on fingerprints and DNA. I guess it was pretty easy using the extensive database they have, and Sayoc's prints were on file from a previous arrest.
He could face additional federal charges in Florida, D.C., Delaware and California (where the targets lived), and maybe state charges in those jurisdictions as well. If they can prove he intended to kill any of them he possibly could be charged with attempted murder under those states' laws after the feds get done with him.
It's always quid quo pro with Donnie Fungus, and this guy can't isn't in a position to pay him or do him a favor.
It seems to me that a prediction Trump would never do something guarantees he will.
There is no bottom to how low he can go.