Like he really liked her, as we used to say in high school. Like he missed her. Like it wasn't just about sex. She also applauds the way he's running the country. They're the bad guys, not her Bill.
Rationalization can be wonderful, especially when it works.
The 'enemies' thing is a very, very powerful and unifying force. Her attitude, friends say, is that enemies are enemies for life and should be consigned to the outer darkness, then vaporized. Even before Ken Starr, other mutual forces of evil served as a marital bond. It was a favorite topic. Ready for combat.