Well, how many Democrat or more liberal voters would vote for Trump? Theoretically a 3rd party or independent candidate can win election, but so many people automatically vote for one of the two major parties.
Perot got 19% of the vote against Bill Clinton. Clinton got only 43% of the vote but won overwhelmingly in the electoral vote because he carried a number of individual states in the electoral college even though he got less than 50% of the vote in those states.
And Perot got maybe 8% or 9% his second go round.....
What would be their incentive for doing so when Hillary is sitting there awaiting coronation?