The field of Republicans seeking the nomination for the Presidency is beginning to narrow, whether any of them pulls out now, or later. Just follow the money. Obviously, Donald Trump will be in the race until the last primaries in June, 2016 because he does not need anyone's money to stay in the race. Ben Carson and Ted Cruz are getting the most support as Outsiders. Jeb Bush continues to get support, for the time being as the Establishment Candidate; however even though he has a huge PAC with over $100 million sitting there, his supporters will disappear if he wins none of the first four primaries early next year.
And, unless something changes between now and next February, this Blogger is willing to predict that Bush will not win any of the first 4 primaries. And, again unless something radical happens, it sure looks like the Republican Candidate for President will either be Trump, Carson or Cruz, with one of them ending up on the ticket as Vice President. The scenario is easy to see. Which ever of these candidates goes to the Convention with the most Delegates is likely to be the nominee for President.
If that person does not have the numbers needed to win outright, then in combination with one of these other candidates as Vice President, the deal is done. Trump would never accept a number two spot. So, if Trump has the most Delegates; but not the number needed to win, he just picks one of the other two to put him over the top. However, it is possible that Cruz and Carson could get together to stop Trump, since they too will have Delegates at the Convention.
If Establishment Republicans try any shenanigans to give Jeb Bush the nomination, it will be end of the Republican Party. Trump will rip up his pledge not to run as an Independent and if he does that, there is no way a Republican will be elected President. It is just that simple.