Republicans supposed "disadvantage" in the popular vote is oversold. Any plausible Republican nominee *not named Donald Trump would have won the popular vote against Hillary Clinton in 2016, and said Republican would have probably been reelected (with a popular vote mandate) in 2020.
I actually doubt that. IMO Trump had an unusually good matchup against Clinton, he was able to portray himself as an outsider fighting a corrupt elitist. I think Clinton would have narrowly beaten Rubio or Jeb, though they would have won Florida by more. Not sure about Kasich.
Here's how I imagine a Clinton vs Rubio race going:
1) Rubio leads comfortably throughout the summer and has a near-double digit lead coming out of the conventions
2) Clinton starts to chip away at Rubio's support as he makes more gaffes
3) Rubio absolutely faceplants at the first debate
4) The stuff about Wainwright Park and Angel Barrios comes out and starts getting traction online
5) Rubio still wins the EC, albeit underwhelmingly and well short of what the polls showed a few weeks before the election, while losing the PV. He comes into office with no mandate (or a very weak one) and can't get much done during his presidency.
