Report Abuse for one-to-three of the worst posters each day. In a week or two, you'll see a better board, especially if two or three of the good posters report abuse. Give one-star to demote any political that makes it to the five-star page with five-stars. Put them on Ignore if truly awful.
Abuse categories: Directing you to a political web site from a stock board is Spam. Derogatory Language (name-calling, insults, hate language) and Obscenity can also be reported. Yahoo does not do anything about a bad poster until they are reported; their punishments escalate each time they are reported (longer and longer suspensions after the initial warning)