Nearly every Republican will vote for Trump. Meanwhile, the Democrats are notoriously fickle already, and have to convince enough independents to vote for them, and they're doing everything in their power to alienate people in both camps.
Typical establishment hubris. The other side supports fascism, so we dare you not to vote for us, or just the assumption that enough people support them out of the gate to win (like Hillary Clinton). And we are fucked by the two party system again.