Mofu Hi,
ultimately it is up to you. If you're not able to block specific advertiser URLs, or locate the URLs, but also don't want to show political ads then you would want to leave the politics category off. Of course, you'd then have to live with a drop in revenue.
My suggestion would be to enable political ads again, and if you see any ads from a political party you're wanting to block, make a note of the URL and block the advertiser from showing further ads on the site.
As mentioned though, this is up to you!