Notice the liberals attacked him when he was still in the G.O.P., but now, not unlike McCain, he is a "maverick" or some such nonsense.
When he was Republican, he was the dumbest kind of paleocon, IMHO -- the sort that called FDR a "war-monger" for pushing us towards involvement in WWII, which was always inevitable anyway. People like that would've been perfectly happy to see Eastern Europe under permanent Nazi control and London bombed into the Stone Age. It's not just isolationism, it's escapism.