By the rules of royal succession — and the voting habits of the Republican electorate — Jeb Bush should be the 2016 Republican nominee.

For five decades, you could make good money simply betting in the GOP presidential primary on the establishment candidate whose "turn" it was. But that rule no longer seems to apply. Jeb, despite the history, is hardly inevitable. He's not even the frontrunner.

Here's a brief history of the contested GOP primaries in the last half century:

In 2012, Republicans nominated Mitt Romney, who four years earlier had won the second most states (11) and the second most popular votes (4.7 million).

Republicans in 2008 nominated the candidate (John McCain) who in the previous open GOP primary had won New Hampshire and finished second on the score of the national popular vote, with 6.1 million.

In 2000, Republicans didn't pick the previous runner-up (it was Pat Buchanan, and he was running on the Reform Party ticket). Instead, they went the European primogeniture route: They selected the oldest son of the most recent Republican President.

Bob Dole was the runner up in 1988, and then the nominee in 1996. George H.W. Bush was the runner-up in 1980, and became the vice president and then the nominee in 1988. Ronald Reagan was the runner-up in 1976 and the nominee in '80. Richard Nixon won in 1968 as the most recent Republican vice president, and thanks to a sense he was robbed in 1960.

That leaves Barry Goldwater, in 1964, as the most recent exception to this rule.

This time around, it seems Jeb Bush is the establishment candidate who's next in line — being the second oldest son of George H. W. Bush. (Rick Santorum, as the runner-up four years ago, can make a claim to the throne. But unlike Dole, McCain, Romney, Bush and Bush, Santorum certainly lacks establishment backing.)

So why should this time be any different? Why shouldn't Republicans just make the easy establishment pick as they always do?

There are plenty of reasons.

First, the Tea Party injected a persistent anti-establishment fervor into the GOP. There are senators today named Cruz, Rubio and Rand Paul because of a conservative base that has become increasingly comfortable with defying the party establishment in their respective states.

Of course, the Tea Party couldn't beat Romney in the 2012 primaries, so what's different from four years ago? For one thing, 2012 served as an additional reminder that picking the "electable" establishment candidate doesn't promise victory in November.

Think of it this way: If you line up the last 10 GOP nominees in order of the conservatism of their campaigns, the guys who won the general election are generally at the right end of the scale (especially Reagan and W.), and the losers tend to be at the Left end (especially Dole and post-tax-hike George H.W. Bush). Republican voters no longer believe more moderate equals more electable.

Candidate quality, however, might be the biggest difference between 2016 and 2012. The Not-Jebs in 2016 all appear — at this early stage — to be stronger than the Not-Mitts were in 2012. Michele Bachmann, Rick Perry, Herman, Cain, Newt Gingrich and Santorum were all worse candidates than the weakest of Rubio, Walker, and Cruz. Carly Fiorina, Rand Paul and John Kasich are probably also stronger candidates than any of the 2012 not-Romneys.

Most importantly, Rubio, Walker and some of the others can plausibly make the case that they are more likely to beat Hillary in the fall than Jeb is. For starters, none of them has the last name "Bush."

Walker and Rubio — and possibly Kasich and Fiorina — straddle the Tea Party-establishment divide in the GOP. Many pragmatic GOP voters will find themselves choosing between Jeb and Walker or Jeb and Rubio. That's a very different choice than Huckabee vs. McCain or Buchanan vs. Dole.

Also, the fundraising picture has been dramatically decentralized since 2008 thanks to Citizens United, and it has even changed since 2012. While Santorum in 2012 could draw on the wealth of billionaire Foster Friess, this time around Rubio, Walker, Paul and Cruz could draw support from more advanced outside groups and fundraising networks. Rubio, Paul or Cruz could enjoy the backing of the Club for Growth in the primary, which would be a strong counterforce to the establishment money machines that will probably back Jeb. If the Kochs can rally much of their political network behind a conservative candidate, they could swamp Jeb money-wise.

Jeb, in the old version of the GOP, would be a lock for the nomination. But this is not his father's Republican Party.

Timothy P. Carney, The Washington Examiner's senior political columnist, can be contacted at tcarney@washingtonexaminer.com. His column appears Sunday and Wednesday on washingtonexaminer.com.