What standard of proof of "facts" should be used in political speech?

In courts, we require proof beyond a reasonable doubt, for example. In physical sciences, there are other standards of proof. But in politics, what constitutes “proof” of a “fact?”

We have organizations like “factcheck.org” and apparently there are Republican backed competitors because they don’t like the way factcheck.org checks facts.

Is it even possible to have a “fact” in politics? Or can we only see the world through an ideological lens (liberal, conservative, non-aligned, etc)?

I’ve worked the bulk of my career in a think tank, writing policy papers and doing research on a wide number of issues. We always tried to make our work transparent, so that if you didn’t like an assumption, you could change it and our analysis would spew out a new number. But these days it seems that doesn’t matter. Transparency is just as bogus as being a hardened political hack spewing catch phrases.

How did this happen? Is there any way to agree on what a fact is, in politics?