There is a priority security line at ORD but it's hit or miss; due to the large number of UA elites based at ORD, and the large number of non-status passengers in paid F on UA, the priority lines can be longer than the regular lines. I can't remember off the top of my head which terminal US is in but there are two or three security gates from this terminal that all dump you in the same place on the other side, so it's worth a walk down to see if one has a shorter line. Sometimes the closest one is backed up to the ticket counter but the next one down to the left has got tumbleweeds blowing across it.