Every Democrat supports Trump
Quite a lot of democrats supported Reagan too. Hence the name: Reagan Democrat.
No, neither in the sense that you are implying, nor in reality. What is fairly likely, however, if Trump gets the nomination, is that a larger block than usual will cross party lines to vote for a celebrity that they admire. (How "Arnold" won in California, after it basically passed to the Democrats politically.) Remember that a huge percentage are not really ideological.)
A still larger block of Democrats would vote for Trump as a Third Party candidate.
Of course the downside, for either Trump or Cruz or any other actual Conservative, is that a large number of the Eastern faux "Liberal," variety of Republican will join a Republicans for (whomever the Democrats finally nominate--almost certainly someone not yet even mentioned). This was not the most important factor that sabotaged Barry Goldwater, but it was a major factor in 1964.
Trump can, of course, offset the loss of the Republican Left--either as the Party candidate or as a Third Party candidate--by some careful appeals to various neglected considerations, which were not available to Barry Goldwater in 1964. (Being deliberately opaque on that subject, so as not to stir up something that would interfere with some work that I must get to this afternoon.)