After 9/11, stricter USA entry controls were introduced but obviously not strict enough for the new President. Unfortunately, the American people don't seem to know what they want or perhaps they have short memories.
This new travel policy is a good idea but appears to have been poorly executed and communicated. You only have to look at Germany to see what can happen with an "open door" policy. Unless I'm being thick, I can't understand why Mo Farah has said he may not get home. If he's got the correct visas and proof of residency in the USA then he shouldn't have a problem. I would have thought better of him if he'd just kept quiet and contacted whoever he needed to, to verify his status.