Group A: Nixon, Reagan, Bush 41, Dole, McCain, Romney.

Group B: Goldwater, Bush 43.

What’s the difference between Group A and Group B?

It’s often said that Democrats fall in love, Republicans fall in line. This translates to Democrats tend to turn their backs on their presumptive nominees while Republicans tend to coalesce around theirs. By a year to 18 months out from primary season, a front runner tends to emerge for each party’s next nomination. History shows that when a party has an open primary (i.e. when it does not have an incumbent to nominate), Republicans will usually nominate their front runner and Democrats will become enamored of a new face and nominate him or her (McGovern, Carter, Dukakis, Clinton, Obama).

So if you’re a Republican, just what does it mean to be the candidate at the head of that line, the one that your party’s voters will embrace and tend to nominate? That is, are there identifiable components or characteristics that might be of some predictive value in analyzing to whom Republicans might embrace this time around? The most obvious component is to be leading early in the polls. In other words, a front runner status, for Republicans, becomes a self-fulling prophesy. Having been confirmed as the front runner in the polls, means you’re a winner and someone to fall in line behind.

So, back to the two groups above. They are all the Republican nominees from 1960 to the present. Is that the difference? Group A nominees all dominated the polls early and Group B did not? Nope.

In 1964, Goldwater was indeed being outpolled by Nelson Rockefeller for several months until after the start of the primary season. Bush 43, however, did dominate the polls from early on through the primary season. McCain and Romney, like Goldwater, languished in the polls up to the start of the primary season and even thereafter. McCain was sometimes as low as fourth place, with Giuliani dominating the field for a long time. Romney of course had four different candidates outpolling him.

The feature that sets Group A apart from Group B is that all of the nominees in Group A had run previously on their party’s national ticket before being nominated in a later year. Neither Goldwater or Bush 43 had. Still, many of the eventual nominees were also long run poll toppers who rode their standing in the polls through to the nomination. This includes all of the above except for Goldwater, McCain and Romney.

So, for Republicans, a truly open primary is one where there is no previous national ticket candidate running for the nomination–which makes this year’s primary as open as those in 1964 and 2000, since none of the candidates have been on the ticket before. If it’s more like 2000, Trump is looking like the nominee and the latest poll (taken 3-6 January) still has him in a commanding lead nationally. Ipsos/Reuters says he is the choice of 41% of Republicans, his highest percentage since a month ago. Cruz, in second place, polled at 15%. Bush 43 led overwhelmingly throughout the period leading up to the primaries.

If this year starts to look more like 1964, on the other hand, Cruz seems the more likely Goldwater of 2016 than any of the other candidates. Both were/are insurgent anti-establishment figures.

If the contest this year boils down to a two-person race between Trump and Cruz, hard to believe, but Republican voters’ choices may well be between a guy dumber than George W. Bush and a guy crazier than Barry Goldwater.