That's the problem? The fact that you take a site at face value regarding its fact checking score, which could be totally BS, partisan, inaccurate, etc., in real life, isn't a problem?
>But look at the above graphs. If PolitiFact was clearly biased, they wouldn't be as wide ranging as this.
That still leaves two ways it can be partisan (or, off) wide open:
1) It can be partial to the shared assumptions/ideology of both parties (who are more alike than different compared to how parties are in other western countries).
2) It can be partisan to one party, and still mark as "bad liars" its people -- only for that party it does it for second players, whereas for the other party it does it for the leadership and first-rate players.
This still gives a total like "here, we have reported on 100 lies from Democrats and 100 from Republicans" thus we're impartial, while still hurting one or the other party far more.