Some time ago, I noted how partisan debates on foreign policy have been for a long time. Now there's a good article in the Weekly Standard explaining why partisanship is here to stay. Gary Andres cites some political science research arguing that party polarization is caused by a sorting process that made districts more homogeneous and the parties more ideological. But secondly, that empowered party leaders in Congress who delivered for the home team.
These are persuasive explanations to me. And I agree with the view that pundits' calls for bipartisanship as an unalloyed good thing are naive and romantic.