President Obama threw Russian spies out of the US. As payback, Russian hackers could have taken down the US Customs computer system on the busiest travel day of the year causing them to go manual.
All as a cover to a fresh team of spies arrival at US airports slipped thru the system to do their tasks in the US just as undocumented people instead of known Foreign Diplomats.
Using Internet connections in the US instead of foreign IP addresses which would easier to trace and harder to filter out. Trump did say something about the hacking would soon be coming to light.
It could be happening here and now!