What I would like is for them to show him the evidence and then see what he says.

I think there are actually 3 different cases:

• Knows what is true and chooses to say a falsehood. This is your normal person lying, which usually comes with subtle indications which can be spotted by the observant that they're lying, such as them turning their eyes away when lying, because the person knowingly lying feels guilty.
• Couldn't care less about what is true or false when talking to other people, so say whatever benefits them most to say. This is sociopaths, psychopaths and narcissists such as Trump: for them talk is just a way to get others to do what's best for them and truthfulness is irrelevant and unimportant, so they fell no guilt at all from lying since lying or telling the truth is all the same with possibly an intellectual consideration that there is no long term tisk of personal negative impact over the long run due to loss of trust when telling the truth so in that case they might refrain from telling a falsehood.
• People who have visions, see things that aren't there or, more commonly, have a strong emotional binding to some tribe and have been told things, interpretations of things or conclusions by leaders of that tribe and refuse to even examine them mentally to determine their truthfulness. This is were you find the outright insane and the deeply religious, but also the members of political, national and even sports tribes. They genuinely believe that what they are saying is the truth, mostly because they didn't checked those truths for consistency or for "does the source of this stand to gain if I believe it" (I.e. cui bono). This is were you find many of the medically insane, people who believe in populist politicians, deeply religious types and people who will believe in any old bollocks from the politicians from "their" side even when they're not generally deemed populist politicians.

Anyway, my point being that the most of the lying on really important shit is coming from the 2nd group or the 3rd group, since normal people who truly know that what they would say would be a falsehood don't like how it makes them feel so tend to refrain from doing it, whilst members of the 2nd group only consider truthfulness-vs-falsehoods in purely intellectual "what's best for me to say" terms and those on the 3rd group actually believe what they're saying (hence feel no guilt in saying it) because they're unable or unwilling to examine, evaluate and judge for truthfulness statements coming from certain sources - they have no intent to deceive but they are none the less doing it because by purposefully refusing to evaluate and judge the truthfulness of certain things from certain sources they've first allowed themselves to be deceived, so when they parrot those things, in their mind they are telling the truth.