Any scenario? The R's have won the popular vote once since 1988. All three of their EC wins since then have been by either a single state (FL in 2000, Ohio 2004), or a string of less than 1% wins in 2016. Trump's approval is stuck in the -10's despite a strong economy.Democrats are in a bind. Choose Warren and they lose their big money Wall St. support. Choose Bernie and run a guy who openly tells the middle class that their taxes are going up to pay for anything and everything, citizen or not. Choose Joe and run a guy bordering on senility. Choose Pete and risk losing a huge chunk of their identity politics voting bloc. They know they are in deep trouble and thus the frenzy to get Trump out by any means necessary prior to the election. Barring some smoking gun on Orangey, I can't see any scenario in which any of the above defeat him in an election.
Do all of the Dem candidates have flaws? Yes. Can Trump win? Yes. But "I can't envision any scenario where he loses" is beyond over the top.