With 63 days until the Iowa caucuses, 71 days until the New Hampshire primary and 92 days until Super Tuesday, the race for the Democratic nomination is in the home stretch. The one thing money can’t buy a campaign is time. And time is running out for everyone except the top tier candidates.

Math and history favor the one who wins at least one of the first contests and Super Tuesday. Today that means the race is between Sen. Elizabeth Warren and Mayor Pete Buttigieg.

For all the talk and wishful thinking that the race is wide open, it has been remarkably consistent. The current top tier, Warren, former Vice President Joe Biden and Sen. Bernie Sanders, have been there for much of the year. Buttigieg returned to the top tier after an earlier appearance last spring.

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Much media coverage focuses on national polls but it is the first contests, specifically Iowa and New Hampshire, that tell you where the race really stands.

The latest Des Moines Register poll, the gold standard for the Iowa caucuses, has Buttigieg in first place at 25 percent, a meteoric 16 percent rise since September. Warren, who led the September Iowa poll with 22 percent, slipped to 16, while Biden and Sanders are tied at 15 percent. The Register poll had the same four candidates in the top tier five months ago.

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In New Hampshire, the most recent poll, conducted by Suffolk University, has a tight four-way race: Sanders at 16 percent, Warren at 14, Buttigieg at 13, and Biden at 12. Since the Suffolk poll in August, Buttigieg has gained seven points, Biden lost nine and Sanders dropped one. Warren stayed the same.

Clearly, Warren and Buttigieg are poised to win either one or both of the first two contests. Historically, a candidate who wins the first two contests runs the table. John Kerry, in 2004, was the last candidate to accomplish this.

The Democratic primary contests since 2004 have been a tussle between two candidates, Hillary Clinton and Barack Obama in 2008 and Clinton and Sanders in 2016. In both cases, the nomination was settled on Super Tuesday. In fact, from 1988 to 2016, the winner of Super Tuesday became the Democratic nominee.

That is even more likely in 2020. Fifteen states, about a third of the country, including California and Texas, will vote on Super Tuesday. Not only will the math make it a challenge for anyone to catch a front runner after that day, but a rule change makes it even harder. At the convention next year, only pledged delegates will be eligible to vote on the first ballot.

To win the nomination a candidate must have 1,919 delegates. To avoid a second ballot that means pledged delegates as super delegates can’t vote on the first ballot. The first four contests – Iowa, New Hampshire, South Carolina and Nevada -- offer a total of 135 pledged delegates. But there are 1,163 pledged delegates up for grabs on Super Tuesday. That’s not enough to be the nominee, but doing well on March 3 can make a candidate almost impossible to catch.

Democratic primary contests since 2004 have been a tussle between two candidates, Clinton and Obama in 2008 and Clinton and Sanders in 2016. In both cases, the nomination was settled on Super Tuesday.

Biden leads in the national polls but he doesn’t lead in Iowa and New Hampshire. Losses there dramatically lessen his chances of winning Nevada or South Carolina – and the nomination. Voters see him as an insurance policy as they wait to see if another candidate emerges to take on President Trump.

Sanders’ prospects are just as precarious. His best chance is New Hampshire, a state he won by 22 points over Clinton in 2016. Today, he holds a slim two-point lead. A loss there means Sanders loses the nomination.

The likelihood of losing the first two contests isn’t the only thing Biden and Sanders share. Their drop in the polls has benefited Warren and Buttigieg. Warren’s rise was fueled by picking up Sanders supporters. Now, former Biden supporters are boosting Buttigieg’s rise.

That is why the contest today is between Warren and Buttigieg, with the senator having the advantage. Despite her recent drop in the polls, Warren is the strongest candidate in terms of fundraising, organization, message, policy positions, and events. Her campaign built a solid foundation out of the adversity she faced earlier in the race, and which she also faces again.

It appears Warren’s recent drop in the polls coincides with her "Medicare-for-All" policy. There is no other explanation for it. But the experience of building her way into the top tier earlier this year should serve her well as she works to regain front-runner status.

Buttigieg is in the top tier and spotlight for the second time, but he returns without the foundation of Warren. He was initially boosted by big fundraising hauls, which have continued. But he didn’t fare well under the bright lights of scrutiny and dropped back into the second tier. His problem with race as mayor of South Bend continues, presenting the biggest obstacle to winning the nomination. Without African American votes, which are critical on Super Tuesday, you can’t win the Democratic nomination.

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Compounding Buttigieg’s problems are his changing policy positions. Just one example is being for “Medicare-for-All" before he was against it. But Buttigieg’s rise is undeniable. The question is whether he can stay there this time.

For now, though, entering the home stretch for the Democratic nomination, the matchup to watch is Warren vs. Buttigieg. Buckle up.

CLICK HERE TO READ MORE BY MARY ANNE MARSH