Trump is bottling it, isn't stepping up to the pressure.
I don't think he's bottling it at all, he's just not thinking. Trying far too hard to get in and clear up all the time, rather than picking his shots better. Missed the blue in one frame when a safety would have been the better choice, Higgins left on the reds and cleared up. Missed the brown because he was trying to put so much side on it to come down for the reds, Higgins left on the reds and cleared up. Then took the black on with so much power that the cue ball ended up miles away from the pack, Higgins cleared up.
He's been doing it all week and getting away with it, so he obviously thinks he should carry on that way. But this is the final, and trying to make every single shot rather than being a little more clever about it is going to put him right up against it. Higgins won't believe how easy that last session was, and you can guarantee he'll be hoping Trump carries on trying to pot everything from any angle he can.