05:44 - Source: CNN
Mark your calendar: 400 days until Iowa Caucuses
CNN  — 

Iowa and New Hampshire, the first two contests of the primary season, have traditionally been key for presidential contenders. This year, though, a lot of Democrats are talking up the importance of contests with a more diverse electorate, like California, Nevada and most importantly, South Carolina.

It is true that connecting with black and Latino voters, who together make up more than a third of Democratic voters, will be key for anyone who wants to be the Democratic nominee. But make no mistake: history suggests that the eventually nominee will likely have to do well in the Iowa caucuses or the New Hampshire primary.

Let’s look at the 16 presidential candidates nominated by the Democrats and Republicans in the modern primary era in the years when an incumbent wasn’t running. Only two of them won their nomination without winning Iowa or New Hampshire.

Now, it’s not as if you must win these early contests. You probably need to come close though. George McGovern won neither in 1972, though he placed second in both Iowa and New Hampshire. Bill Clinton didn’t win either in 1992, though Iowa was ceded to home state Sen. Tom Harkin and Clinton came in second behind Paul Tsongas in New Hampshire. Put another way, no one has won a major party nomination since 1972 without coming in the top two in either Iowa or New Hampshire.

Even though McGovern and Clinton didn’t win, their candidacies are instructive on why Iowa and New Hampshire are important. The press generated from doing well in these states can be huge. McGovern’s second place finish in Iowa resulted in positive headlines for his campaign, and he was able to overcome Edmund Muskie’s early advantage in the national polls. Clinton was able to declare that he was the “Comeback Kid” after his second place finish in New Hampshire and ride it to primary success.

Studies show there can be a large momentum effect from doing well in Iowa or New Hampshire. A 2010 study from Brian Knight and Nathan Schiff found that these early contests have up to five times the influence of later contests because the momentum the two states can generate.

Barack Obama’s 2008 campaign, which may be a roadmap of sorts for those hoping to win big in South Carolina, where black voters play an important role in the primary, shows the momentum effect in full force.

Before Obama won Iowa, he was neck-in-neck in the South Carolina polls with Hillary Clinton. Immediately after winning Iowa, Obama jumped out to a double digit lead against Clinton in South Carolina. He never surrendered that lead and easily won the primary. Without taking Iowa, Obama could have very well lost South Carolina and the nomination.

Now candidates trying to win in a crowded field have previously tried to nationalize the run for president. It didn’t work. Democrat John Glenn, who was second in the national polls, tried to do it in 1984. He didn’t come close to winning Iowa or New Hampshire, which all but ended his campaign. More recently, Rudy Giuliani, who was leading national polls but not polls in Iowa or New Hampshire, tried to rely on Florida as a backstop. Giuliani’s lead in Florida, which hosted the fourth primary on the calendar, disappeared after he was blown out in Iowa and New Hampshire.

Crowded primaries, like 2020 is shaping up to be, are especially susceptible to momentum effects. If there is no clear frontrunner heading into Iowa or New Hampshire, any win will probably be seized upon by the press. That’s exactly what happened in 2004 when John Kerry turned a wide open primary into a blowout by taking Iowa and New Hampshire.

Of course, it’s not just about momentum. Although Iowa and New Hampshire lack racial diversity, they look a lot like the national primary electorate in other ways. They have similar age and ideological breakdowns to other primaries. Iowa has fewer independents voting in its caucuses than the national average, while New Hampshire has more. Finally, because the Democratic electorate is majority white, Iowa and New Hampshire let you know if you’re connecting with a majority of Democratic voters.

Now could the 2020 Democratic nominee break the mold? Sure. We’re not dealing with a huge sample size of previous primaries. Social media, which is in some ways an equalizer, may keep candidacies alive for longer than they may have previously have been able to. Bernie Sanders stayed in the 2016 race much longer than he probably would have been able to in previous years because of money raised online. And remember, President Donald Trump has broken many rules that we thought would stand the test of time.

Even Trump won New Hampshire, however.