William F. B. O'Reilly Portrait of Newsday/amNY columnist Bill O'Reilly (March 28,

William F. B. O'Reilly is a consultant to Republicans.

It doesn’t take a genius to see where the Republican presidential primary stands today.

Donald Trump has just under a third of the electorate’s support based on polling, and the other four candidates in contention are splitting up the rest — former Florida Gov. Jeb Bush, Texas Sen. Ted Cruz, Ohio Gov. John Kasich and Florida Sen. Marco Rubio. Ben Carson is, for all intents and purposes, out of the race.

Of the four non-Trumps remaining, Cruz has the best chance of eating into Trump’s base. Like Trump, he’s a clear outsider. And unlike Trump, he’s an actual conservative.

More coverageOpinion and analysis about the 2016 presidential campaign

Cruz and Trump are going to fight it out until the bitter end for the most-disaffected Republican vote. Bush, Kasich and Rubio are competing for the rest, which should constitute a plurality in a three-candidate race. But for that to happen, two of these three “establishment” candidates will have to drop out.

Who are they going to be?

Kasich has momentum coming off a strong second place in New Hampshire. But he lacks money and campaign infrastructure heading into the Southern state primaries.

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Bush remains wobbly after placing fifth in New Hampshire, but he can’t be counted out. He could be a safety pick for a lot of people alarmed by the instability of the discourse this election cycle.

Rubio suffered a devastating blow in the final New Hampshire debate. But he’s still arguably the strongest of the three. He’s a natural born orator, and he’s a darling of movement conservatives. He should be able to get back on his feet.

One scenario that’s been bantered about is a Rubio-Kasich ticket. It makes sense for a lot of reasons. Rubio’s weakness is that he lacks gray hairs. Kasich has got them. He’s an old, steady Washington hand who could anchor the passionate young conservative Rubio, who also benefits with many voters because of his Hispanic heritage. On top of that, the pair’s home states of Florida and Ohio will be key tossup states in the general election.

Presidential tickets are seldom announced until the party conventions, but Rubio and Kasich could change that this year. By teaming up early, they could offer both change and stability to the Republican electorate, and they might be able to chase Jeb! out of the race.

The longer the three of them remain in the primaries, the less likely it is that any will win.

William F.B. O’Reilly is a Republican consultant.