partisan

If something is prejudicial towards a particular point of view, you can call it partisan. You'll often hear of the partisan politics in the US — since politicians seem to be so devoted to either the Republican or Democratic parties.

Partisan can be used to describe rabid supporters of any person or activity. In American English, however, it is most often used to refer to politics and the American two-party system of Democrats and Republicans. A bill introduced may have partisan support from the party that introduced the bill, or — more rarely it seems to American voters — the bill may even have bipartisan support. The prefix bi is added to show the support from both parties.