Few billionaires have been more critical of Trump than Bill Gates, which is why it comes as a bit of a surprise that the two of them are meeting today.

It's not known who requested the meeting. It seems unlikely to have been Trump, since Trump tends to run the White House like a reality TV show, which calls for publicizing meetings with famous people with oodles of Trump braggadocio.

If Gates requested the meeting, on the other hand, it's hard to see what he expects to accomplish. CNN has speculated that Gates might repeat the criticisms that he has leveled at Trump in the past.

Specifically, Gates has been highly critical of Trump's "America First" policies, especially cuts to foreign aid and the raising of barriers to free trade, both of which Gates believes to be detrimental to the United States and to the rest of the world.

However, Gates is no dummy, and no doubt realizes that regardless of what he says to him, Trump is unlikely to change his behavior or policies, even if, in the moment, he appears to agree with whatever Gates might have to say.

As I pointed out in a previous post, I've tracked the careers of Gates and Trump closely over the years and have interviewed both of them, so I have a sense of what they're about.

I think that, after the meeting, there will be some kind of announcement--probably about trade with China or perhaps Gates's charitable work--that will ultimately turn out to be a nothing-burger.

That's because the real purpose of Gates's visit is for Gates to assess whether Trump's mental state constitutes an existential threat. I believe that Gates sees a real possibility that Trump will completely screw up negotiations with North Korea, resulting in a nuclear war.

And as Steven Pinker points out in Enlightenment Now (Gates's "all-time favorite" book), nuclear war is one of two true existential threats to our civilization (the other, of course, is climate change).

If Gates concludes that Trump isn't just bluster but a true threat, I strongly suspect that Gates will begin to pump money into getting Democrats elected in the 2018 midterms, thereby counterbalancing contributions from billionaires like the Mercers, who supported Trump's campaign and the campaigns of Trumpish candidates in the past.

There is, however, another possible scenario. Could Gates be considering a run at the presidency himself? If so, Gates might want to have a candid conversation with an outsider who'd already gotten the job.

Buttressing that scenario is the fact that Gates has recently been making the rounds by meeting with the heads of the U.S. allies, specifically French president Emmanuel Macron  last December and German chancellor Angela Merkel last January.

Time will tell, but this much is certain: Going forward, Gates will be playing a larger role in world politics than he has in the past.