(CNN) First things first: The theme song of the week is the closing theme from Knots Landing.

A new Monmouth University Nevada Democratic caucuses poll finds that former Vice President Joe Biden leads with 36%. He was followed by Massachusetts Sen. Elizabeth Warren at 19%, Vermont Sen. Bernie Sanders at 13%, South Bend, Indiana, Mayor Pete Buttigieg at 7% and California Sen. Kamala Harris at 6%.

The poll was the first high-quality poll taken of the third-in-the-nation Nevada caucuses.

What's the point: The big question for most of the 2020 Democratic presidential field is how to beat front-runner Biden.

One obvious way is to change the entire national trajectory of the race. That could certainly occur.

But assuming the national race remains mostly stable (as it has been for the most part ), you'll have to knock Biden out state by state.

And to that idea, Monmouth's Nevada poll reinforces a key point: to beat Biden, you'll likely have to defeat him in Iowa and New Hampshire. If you don't, the primary calendar only gets easier from there for him.

History has been quite kind to national front-runners who win Iowa or New Hampshire. Take a look at the national polls in competitive primaries on the eve of the Iowa caucuses and who won since 1972. In competitive primaries, the national front-runners who have won either Iowa or New Hampshire have gone on to win their party's nomination 11 of 13 (85%) times. Perhaps not surprisingly, the two contests (1972 and 2008 for the Democrats) where a national front-runner won Iowa or New Hampshire and didn't win the nomination were also contests which featured the lowest national primary vote margin for the nominee.

Compare that to contests where the national front-runner lost Iowa and New Hampshire. In those primaries, the national front-runner won only 1 out of 5 times (20%). The one time the national front-runner won, despite losing Iowa and New Hampshire, was Democrat Bill Clinton in 1992. That year, Iowa was uncompetitive because home state Sen. Tom Harkin was running, and Clinton was able to call himself "the comeback kid" following his second-place finish in New Hampshire.

These stats get at something important: presidential primaries are sequential. Voters nationally tend to heed the advice of early state voters. If Biden is able to emerge from the early states with at least one win, it'll be difficult to convince voters in later states to change their minds.

This year, especially, Iowa and New Hampshire provide unique and fertile ground to knock the front-runner off his perch. Our CNN/Des Moines Register/Mediacom poll released last weekend of likely Democratic Iowa caucus-goers showed Biden leading the field by 8 points and was at just 24%. That's quite a bit weaker than national polls that have him polling in the 30s with a double-digit advantage. Biden's advantage in New Hampshire has, like Iowa, been smaller than it's been nationally.

Meanwhile, his advantages in Nevada and fourth-in-the-nation South Carolina primary have been quite large.

The reason for Biden's weakness in Iowa and New Hampshire is multi-fold.

Both Iowa and New Hampshire feature a more liberal electorate than the national Democratic primary electorate. Biden's been running up the score with self-described moderate and conservative Democrats. He actually trails among liberal voters in Iowa , for example, but more than makes up for it by lapping the field among self described moderates and conservative.

Additionally, both Iowa and New Hampshire are very white. Biden has consistently done better with non-white voters (specifically African-Americans) than with whites. Buttigieg and Warren, specifically, haven't been able to breakthrough with non-white voters so far.

Finally, there's something to be said about geography and the people closest to Biden in the polls right now. Both Sanders and Warren represent states right next to New Hampshire. They're quite familiar to voters in the Granite State. Buttigieg, meanwhile, is the mayor of a city within a four-hour car ride of Iowa.

All those potential advantages for Biden's opponents mostly disappear once the race gets beyond Iowa and New Hampshire. We get into much more moderate states once the South Carolina primary occurs. Nevada and South Carolina are far less white. And once the race goes national, home state or near-home state advantages tend to go away.

The bottom line is this: if Biden wins either Iowa or New Hampshire, he's likely going to be the Democratic nominee.