For what seems like forever we have been waiting for the Trump campaign to come to an end, to reach the point at which the joke will be over and the GOP will pick a real candidate. As you may recall I thought the end of his campaign would come when the actual voting began and the lack of a ground game and professional campaign organization would catch up with him. Unfortunately to knock Trump off his perch there is another necessary ingredient that has not materialized: an alternative candidate who isn't complete garbage. There remains a chance that Republicans can rally around one of the others – most likely Rubio, whom I argued five years ago was the only candidate in their field with any semblance of personal appeal. But the window in which that could happen is diminishing.
In the future we may look back at the Jeb! campaign as one of the most spectacular failures in the history of American politics. One got the impression all along that he was their Mitt Romney-esque fallback option, that if none of the other candidates caught fire the big money people behind the party could go with Jeb! and at the very least feel confident that he wouldn't screw anything up too badly. His ineptitude as a candidate took everyone by surprise. He proved incapable of generating any momentum despite his massive bank account and near-universal name recognition. Imagine Hillary Clinton spending $150 million and never finishing better than 4th in a primary and you get the picture of what Bush managed to do.
The stunning failure of their empty vessel / cipher / hereditary heir apparent has left the GOP scrambling, though. Trump's level of support is what it is, and if the party could unify behind one other candidate he remains beatable. But which one? Jeb! was abysmal. Rand Paul was a non-starter. Recycled evangelical puds like Santorum and Huckabee never got off the ground. Christie was never taken seriously. Fiorina sounded good on paper but whenever she opened her mouth everything in the room died. Kasich is far too dull and too "liberal" (the imaginary GOP version of liberal) to appease competing factions in the party. Carson really isn't even running. That leaves Cruz, who looks like a cut-rate mortician and sounds like the lunatic he is, and Rubio, who can't seem to do anything except repeat canned phrases interminably.
Now that we are down to four candidates (excluding Carson) and one of them is not acceptable to the GOP base (Kasich), look for the big right wing donors and the RNC leadership to throw their weight behind Rubio, or perhaps Cruz, in a last ditch effort to save themselves from Trump. The more they dither on choosing between the two, the higher the chance that it will be too late by the time they act. In an ideal GOP scenario, Cruz would accept some kind of concession to drop out and leave Rubio as the last man standing in opposition to Trump. If the political class was able to sell George W. Bush as a bootstrap-pulling cowboy then there is no reason they won't be able to sell Rubio as some sort of charismatic young go-getter.
There is no reason at all to feel sympathy for them; metaphors about reaping and sowing come to mind. The GOP establishment made Donald Trump. It had dozens of opportunities to push back against the insanity of some of their supporters and they chose instead to fan the flames for short-term benefits. That paid off in 2010, but now the true long-term costs are becoming apparent. Couldn't happen to a more deserving bunch of hacks.
By the way, on the point of timelines: if an independent candidate wants to enter the race that decision will have to come very soon. Ballot access rules vary by state but some deadlines for appearing on the November ballot are approaching. Jumping through the many hoops set out to disadvantage third party and independent candidates takes time, and in most states a candidate would have to get tens of thousands of signatures very quickly. If that decision hasn't been made by March 1 the window in which it could be practical may close.