Probably at the top of the ladder and came face to face with the rifle armed nut who -heard- him climbing an aluminum ladder leaned against a steel building. No good way to get up there silently, and in a hurry, and get the drop on the bad guy. Sometimes all you get is a bad deal and you do your best.
And at the very moment EVERYONE there knew and they left Trump onstage.
We know now that the ladder was a permanent installation for roof access. It was not blocked, this is another key to understanding the true nature of this act of political treason.