bill: Suppose in 2016, Trump ran as a democrat. He was Hillary's only opponent and he was the Bernie Sanders of that race (democratic socialist) does anyone think he would be able to win a democratic primary or let alone a general election, and would my democrat friends on this site vote for him.
Your hypothetical does not work as Trump is in 1,000 ways incongruous with both the Sanders and Clinton factions of the party. If we take a step back and ask if we would support a nominee who was unqualified and a terrible human being only interested in himself, destructive to democratic (small-d) institutions, but who would support policies favored by Democrats... I just hope that I am never put in such a position. If the Republican nominee were a reasonable and thoughtful person like Romney or Kasich I would have to think about crossing over.