It is highly unlikely that ANY candidate can win the Presidency in modern America without much support from:

Hispanics

Blacks

Women

Youth

Trump has actively alienated each of these groups at some stage of his campaign, and in many cases multiple times. He has even made alienation of some of these groups a staple of his campaign. This has made Trump perhaps the most unpopular presidential candidate among non-whites in modern American history.

The following favorable-unfavorable ratings are from November 8, 2015, so the ratings are likely even worse today than they were at the time given the level of discourse from Trump since then.

Even the GOP understood that they must garner support from minority groups during the 2016 election cycle in order to stand a chance. See: 6 Big Takeaways From The RNC's Incredible 2012 Autopsy

Trump essentially tore up the GOP's 2016 playbook, doused it in gasoline, set it on fire, then pissed on it for good measure.

Trump's primary success is almost exclusively due to his appeal to white, (mostly male) disaffected nationalists - a particularly angry and vocal subset of the GOP base. While this group may be not only sustainable, but effective for the Republican Primary, it is a death sentence for any candidate's general election hopes. The changing demographics in the US simply don't favor him. There are simply not enough white nationalists (overt racists and/or borderline racists) out there to carry a candidate like Trump to victory.

I predict that Trump will attempt to pivot and alter his message during the general election being the shapeshifter that he is, but I don't see that being a successful strategy. Unlike his current base of supporters who appear to be immune to rampant, pathological lying, general election voters have already seen through his bullshit and will not be so easily swayed by his shifting rhetoric.