If Trump does become the nominee, Republicans will fall in line. Their dislike for Democrats will be enough for them to support him.
I am a 4/4 Republican voter. I am involved in Republican politics. Should Donald Trump become the nominee of the GOP, I won't support him. The last six years have been difficult for Americans in part because of the failed liberal policies of the current administration. A choice of Donald Trump or the Democrats would be a choice of a third Obama term Vs. a more left-wing wacko who because of his stance on one issue appeals to some on the right.
Hillary Clinton would do tremendous damage to our country if she's elected, she will continue the same policies of this administration that have kept our economy in a sorry state and made us more vulnerable in a dangerous world. Yet, Donald Trump would implement policies intended to re-distribute wealth, his trade policies would lead to massive inflation and a depression because jobs would be lost, wages would fall, and prices would rise. I refuse to take part in the decline of the United States. So, I'd vote third party. Unless of course the Democrats nominate Jim Webb, Webb is better than Trump. I am not sure what I'd do if it was Biden Vs. Trump.