Once again, Donald Trump is poised to win an election, and Bernie Sanders appears to have some legs. Prior to the Iowa caucuses last week, I wrote that it was theoretically possible for two populist extremists (Trump and Sanders) to win in Iowa and then go on to win New Hampshire, too. But neither of those candidates won Iowa. Trump appeared to have a big lead going in, but couldn't make it materialize, and Sanders was neck and neck with Hillary Clinton and held true to form, coming in only slightly shy of the lead.

As I showed previously, it would be highly unusual for a candidate to win Iowa and New Hampshire and then not go on to win the nomination — it hasn't happened in my lifetime. And it's not going to happen this year either.

The polls for Tuesday's first primary of the season show Trump and Sanders well ahead — both are nearly 15 points ahead of their next rivals.

Going into Iowa, Trump was about 7 percentage points ahead of Cruz. Cruz wound up winning that contest, and we learned that Trump's support was overestimated by about 8 points. Rubio earned about 10 points more than the late polls predicted. Trump seriously underperformed, while Rubio outperformed many people's expectations. Rubio has again been surging ahead in the New Hampshire polls, but it's unclear whether we should expect him to overtake Trump in New Hampshire, like Cruz did in Iowa. The gap is still a lot to overcome.

It's safe to say that if Trump fails to deliver again, and does not bring home the big trophy on Tuesday, his prospects will be seriously damaged. Likewise, if Rubio outperforms expectations, the momentum may continue to be with him through the next number of contests and into the convention.

On the Democratic side, Clinton hasn't held the led in the New Hampshire polls since last August. It seems likely that Sanders will win on Tuesday, and probably by a wider margin than Clinton did in Iowa. The polls on the Democratic side are more accurate than on the Republican side, because predicting who will actually turn out to vote for Donald Trump is a nontrivial task.

If Sanders wins by a healthy margin, and Rubio surges ahead of Trump, then we'll all be spinning our heads on Wednesday morning trying to figure out how the Democratic side has come to seem like more of a toss-up, with the two main candidates splitting the first two contests, while the Republican side looks like a solid flow towards one candidate — Rubio. Less than a week ago, no one expected the Democratic side to look less certain than the Republican.

That said, Clinton still has enormous advantages over Sanders (endorsements, ground game in upcoming primaries, etc.). But if Sanders wins on Tuesday, the race will be more interesting for a while.

In all likelihood, Trump and Sanders will win on Tuesday, and the show will continue in South Carolina and beyond.

Based on the evidence that Rubio has surged ahead in the invisible primary, and Clinton is now, and has been for some time, clobbering Sanders in that arena, it looks likely that November will be a Clinton vs. Rubio contest.