WASHINGTON (AP) — The first President Bush had one, so did President Bill Clinton, and the second President Bush had two. Now, President Barack Obama wants to build a coalition of nations to join the U.S. to combat the threat posed by the Islamic State group in the Middle East and beyond.

The diplomacy of coalition building is time-consuming, and questions about who can or should join are often messy. And in this situation it is complicated by the fact that the U.S. and its allies share an interest in defeating the extremists with some governments they otherwise oppose. Yet, if politics makes for strange bedfellows, coalitions do as well.