The easiest way to ruin a board is to post in threads on page 10+ to spam the front page with what looks like normal /pol/ activity, except it's all 2-8 days old. Then later, normal users will reply to the thread, keeping it alive well past its normal expiration and relevance.
examples of this can be seen here:
https://8ch.net/pol/res/5499618.html#5547986
https://8ch.net/pol/res/5538911.html#5558784
https://8ch.net/pol/res/5549420.html#5559263
https://8ch.net/pol/res/5537296.html#5554323
https://8ch.net/pol/res/5524104.html#5553244
Therefore, I'd suggest lowering the number of pages on /pol/ to 10 or bumplocking threads that have already hit page 10.