Bolivia because Morales accuses the U.S. of trying to foment a coup against him. Venezuela because Chavez is trying to show solidarity with Morales. Those are the stated reasons, anyway. Story here.
I can’t see us actually going to war with either country*, so I guess the only currently relevant debate is how this will affect the U.S. election and how the candidates will/should respond when asked about it, as they will be.
*Unless there’s a coffee embargo. Then we gonna have to kick some ass!