Trump hasn't divided the party. The party has attacked him, nonstop and ceaselessly, from the moment he entered the race. That he has prospered nonetheless is a sign of the depth of feeling against the Republican establishment. Cruz should have tapped into it. Instead, he is working with the establishment to fracture the party and ensure democrat victory in November. The establishment is fine with that. They just don't want Trump to end their gravy train.
The party has attacked him. Which is another way of saying he’s divided the party. It’s not just a few elites in Washington who don’t want him. The majority of Republicans don’t want him. He’s got a plurality, nothing more. So it will come down to who the folk’s second choice is. There aren’t too many who list Trump as their second choice.