I bounced through a post on the Metro site to one of the documents on the WikiLeaks site that gives a good indication of what the U.S. thinks of Boris Johnson. It's not particularly flattering but this was from 2008. Has there been improvement in the last 8 years? I leave that up to you to judge.

WikiLeaks: LONDON MAYORAL ELECTION: A NATIONAL BELLWEATHER?

Metro News: This is what WikiLeaks revealed about Boris Johnson