Any chance you have Global Entry? That can help with immigration.
If you book your entire itinerary on a single PNR with Alaska then they'll probably take care of you if you misconnect due to immigration. If you booked a F seat then you may have a downgrad on a misconnect so that could be an issue. If you're nervous, call up AS and see what options they have for you. What was your original connect time on the flights?