At this point, I think Senator Rubio will be a major contender in 2020 no matter what happens. If he wins the nomination and the general election, he's obviously got it. If he wins the nomination but loses the general, Mrs. Clinton has proven herself to be a terrible candidate (she's struggling against a socialist, for crying out loud), and the election will almost certainly be very closes in that situation. There's even the possibility of the GOP winning the popular vote but losing the electoral vote. If he loses the nomination, he's already made it this far, so he shouldn't have too much trouble winning the nomination in four years.
Let's put to bed this myth that she is struggling against Sanders. The race is closer than she thought, but he also had a huge advantage in the first two states - demographically and geographically. Let's not forget Al Gore almost lost NH to Bill Bradley, GWB lost NH to John McCain and was scared sh**tless going into SC. All front running campaigns that are non-incumbent presidents face challenges - it's how you respond. She got a 6 point win in a sh**tshow of a caucus in Nevada and is poised for a 20-30 point blow out in SC. She will win almost all of the primaries on Super Tuesday. People are acting like this is some panic stricken campaign falling apart at the seams...