Since 1952, nearly every battle for an open Republican presidential nomination when there has been no Republican incumbent running for re-election has followed two dependable storylines.

First, a year before the party convention, the GOP voters have settled on a front-runner and then, with the only exception being former New York Mayor Rudy Giuliani (who, before he self-destructed his campaign in 2008, led in the 2007 polls), 12 months later, nominated that early front-runner. Beginning with Dwight Eisenhower in 1951 – followed by Richard Nixon in 1959 (and again in 1967), Barry Goldwater in 1963, Ronald Reagan in 1979, George H.W. Bush in 1987, Bob Dole in 1995, George W. Bush in 1999 and Mitt Romney in 2011 – the GOP candidate who won the Gallup poll also won his party’s nomination. John McCain, in 2008, became the only dark horse in almost six decades to win a Republican convention.

The second predictable narrative has been that in choosing a presidential nominee, Republican voters first decide “whose turn it is” to be nominated. The GOP is a little bit like Kiwanis or the Rotary Club. If you were sergeant-at-arms last year and you’re club vice president this year, then you’ll almost certainly be club president next year.

Think about it. Ronald Reagan, who was runner-up to Gerald Ford in 1976, became the 1980 nominee; George H.W. Bush, runner-up to Reagan in 1980, was nominated in 1988; Bob Dole, runner-up to Bush in ’88, won the next open nomination, in ’96. Plausible nominee-in-waiting George W. Bush in 2000 made it “his turn.” And John McCain, who finished second in 2000, went on to win the nomination in 2008, when Mitt Romney, the eventual 2012 standard-bearer, finished second to the senator from Arizona. You get the drift.

But 14 months before the 2016 Iowa caucuses, there is no Republican whose supporters can credibly claim it is his or her turn. In a recent CNN/Opinion Research poll of Republican voters, former orthopedic surgeon Ben Carson – who has never run for office – was the only potential candidate (other than Romney, who led with 20 percent) to break double figures, with 10 percent. Former Florida Gov. Jeb Bush had 9 percent. New Jersey Gov. Chris Christie, 8 percent. Former Arkansas Gov. Mike Huckabee had 7 percent. Sen. Rand Paul of Kentucky and Rep. Paul Ryan of Wisconsin, the 2012 vice presidential nominee, were tied with 6 percent each, while Sen. Ted Cruz of Texas and Wisconsin Gov. Scott Walker both had 5 percent. Former Sen. Rick Santorum of Pennsylvania, who finished second to Romney in 2012, was now preferred by only 2 percent. By contrast, Democrats almost always reject the leaders in the pre-primary polls and end up nominating some semi-unknown underdog. Only twice in the past half-century has the eventual Democratic nominee led a year earlier in the Gallup poll: former Vice President Walter Mondale in 1983-84 and incumbent Vice President Al Gore in 1999-2000. Democratic front-runners Ted Kennedy, Gary Hart, Hillary Clinton, Ed Muskie and Joe Lieberman (that’s right) failed to win the prize. In 1991, then-Arkansas Gov. Bill Clinton, just 13 months before he would become the first Democrat since 1932 to defeat an elected Republican president, slipped to only 6 percent in the Gallup poll. In the entire year before he won the White House, Jimmy Carter did not even register in any Gallup poll.

Historically, the more emotional Democrats have to “fall in love” with their nominee, whereas the more matter-of-fact Republicans have generally been content to “fall in line” behind theirs. It looks as if 2016 will be an unconventional year for both.

Will GOP voters, with no clear favorite and no designated successor, choose with their hearts or their heads? Will Democrats be able to settle and fall in love with the overwhelming front-runner? Stay tuned.

Editor’s note: To find out more about Mark Shields, visit the Creators Syndicate website at www.creators.com.