Donal Trump was actually not topmost liar at the time of sampling, but only 2nd place. Color me surprised.

Both this and the underlying system of fact checking are ignoring the elephant in the room: we have no direct access to the truth. Instead, all we can do is check for consistency. This can be either internal (if I say "two is even" and later "two is odd" I must have lied at least once) or with external source (e.g. look it up somewhere, or ask an expert).

The best external source is reality, if you can corner it with a well designed experiment; this is, unfortunately, really, really hard.

Established theories are also good (but, as history has shown, can be wrong). The biggest problem with theory-based fact checking is that our best theories generally come in pairs that make conflicting claims or are otherwise inconsistent. Plus, the proper application of theories can often be a minefield of subtlety. So this comes down to a choice of "pick the theory that gives the answer you like" or "trust the experts" (e.g. argument by authority).

That leaves us with the most popular option: compare the claim against some consensus (and it happens to be correct). This is generally easy, and works great when there _is_ a consensus, which leads us to overestimate its reliability. And thus we waste years exploring amyloid beta plaques, looking for dark matter, teaching whole-word reading, and so on.

It would be great if we had an easy way to tell who's lying, but in fact what we've got is a lot of ways to tell who we agree with and who we don't, and we don't always agree with each other on that.

Thinking you can objectively quantify the degree a politician is lying is a mistake. Obvious, open, fact-checkable and relevant lies are the minority.