These group aren't stupid.
They won't be impressed with a party that ‘gives’ them the vote then takes it back if they make the wrong choice: the wrong' choice is 'anti-elite Bernie. Clinton was the Establishment choice and she's being rejected.
An 'anti-elite revolution' going on - and it's happening in both parties. Biden's an establishment elite. He doesn't have a chance. He'd do worse than Hillary.
Trouble is, Trump might also be a loose cannon. There is something to be said for a Head of State who is not an example of serial polygamy . . .
Were Cruz to win and Trump to split, the Electoral College might deadlock. Which would leave the Republicans in the House to decide among them, since the vote would be held by state - one vote per state - and the Republicans have a natural gerrymander helping them because of the tendency of Democrat voters to concentrate in cities while the Republican voters are more evenly distributed. Thus, Democrats win the governorship of PA and win the presidential electors - but they win a few House seats overwhelmingly, while the Republicans win the most House seats in PA, by smaller margins.
Thus, even were the Democrats to win a simple majority in the House, Republicans would control the most state delegations unless they really got blown out. And under the Constitution the House could only consider the first three finishers in the Electoral College. In that scenario I would think the House would find Cruz to be least distasteful of the three.
OTOH the Senate could choose a VP other than the running mate of the president selected by the House. And likely would, if the Democrats took control of the senate.