In general in American politics, it is better to be supported by the old than by the young. The young have enthusiasm, and will volunteer and knock on doors for you. The old actually show up on election day.
This strikes me as explaining yesterday's results fairly well. Bernie Sanders has all the enthusiasm: no one at all seems to be enthusiastic about voting for Clinton. Democratic participation is way down across the board from 2008 or even 2012. Bernie is winning young voters by vast margins, but he loses the elections because only a few of the young show up relative to their numbers.
As the enthusiasm of the young is disappointed by watching the corruption of the DNC wash away their icon's chances, how many of them who did make it out to the primary will make it back out to the general? I have already heard three young people I know say that they will not be turning out to vote for Mrs. Clinton in the general. Perhaps they will change their mind. Perhaps not.
Republican enthusiasm is way up. Trump voters especially seem to be both enthusiastic and showing up, suggesting that the enthusiasm for him is with the older voters rather than the younger ones on average -- though there are occasional surprises in Trump's support. But anti-Trump Republicans are enthusiastic too: they are enthusiastic about voting against Trump.
Cruz did well last night relative to all the other non-Trump Republicans. By taking Texas and Alaska, America's most emblematically Red states, he has surely won the right to be the conservative candidate in the race. I think the remaining non-Trump candidates should withdraw, especially Rubio, whose near victory in Virginia was occasioned entirely by his support in the Washington, D.C. metroplex. This is not the year for D.C.'s favorite son.
If you don't want Trump, Cruz is probably the last chance. He's the other candidate in the race who is plausibly an outsider, and who speaks to the anger among the millions of voters who have been backing Trump enthusiastically. If you want that enthusiasm to carry over into the general, and you certainly do if you want to win, finding a way to swap Trump out for an establishment figure is not the way to go. Cruz could win the primary and the general. Trump could, too. Nobody else in the field strikes me as having the chance.