Here's the puzzle at the bottleneck. Don't look unless you've really worked it over. There are some complementary exclusion sets and 2x2 sets in there that took me a few iterations to develop. I don't want to spoil your fun.

Logic-Presidents1.gif
At this point only clues 7 and 8 are left.

Can you figure it out from here? I'll post the key to solving this in a later reply if anyone asks; but not until asked.