Factors that might be thought of as different include 1) the level and penetration of domestic surveillance, 2) the likelihood of spotting a plot before the bomb gets taken to an airport, 3) the availability of explosives.
You forgot the most important one:
0) the number of terrorists.
No terrorists would mean no threat.
Europe is importing many more of them every day, with no end in sight. Trump is at least trying to stop America importing them.