Ahead of the Iowa caucuses last week, candidates and their allies were reminded that history casts an interesting light on the context: plenty of candidates who came up short in the Hawkeye State have gone on to do quite well, just as plenty of candidates who thrived in Iowa ended up failing soon after.
In 2008, for example, John McCain barely tried to compete in the caucuses -- he ended up finishing fourth -- but he nevertheless won his party's nomination with relative ease. In 1988, George H.W. Bush finished third in Iowa -- six points behind a televangelist, believe it or not -- but nine months later he was nevertheless elected president.
The New Hampshire primary, however, is a very different story. Future nominees and future presidents have done well in the first-in-the-nation primary, and those who've finished outside of the top two in the Granite State have, without exception, failed.
We can start with the Democrats, because it's easy: there are only two contenders. Of the last six New Hampshire primaries, the party's presidential nominee has finished first three times, and finished second three times. What does that tell us about Hillary Clinton's and Bernie Sanders' odds of 2016 success? Not a whole lot.
But among Republicans, it's a more interesting story.
In the modern era, the winner of the GOP primary in New Hampshire has gone on to win the Republican nomination with only two exceptions: Bob Dole came in second in 1996 and George W. Bush also came in second in 2000.
How many candidates have come in third or worse in New Hampshire, only to eventually win the Republican nomination anyway? None.
What's more, while no GOP candidate has ever won Iowa and New Hampshire in the same cycle, every Republican nominee has managed to win either Iowa or New Hampshire.
Of course, history offers trends and guidelines, not rules. Just because something has never happened before doesn't mean it can't happen now.
That said, candidates who finish third or worse tonight will have to overcome a historical hurdle if they intend to be their party's presidential nominee. And candidates who've finished third or worse in both of the first two contests should understand they're trying to do something that simply hasn't been done before.