WASHINGTON — There's a version of Bernie Sanders' world in which the Vermont senator is right on track to win the Democratic nomination and take over the larger expanses of the party's coalition.

But there's another version in which he's just living in a two-dimensional political space — trapped with a voting floor and ceiling that are a single line. And the path between the second world and the first may be hard to traverse.

There were stark warning signs for him in each of the first two states on the primary calendar, even though he won the popular vote in both of them.

The most telling trouble spot for Sanders is that he barely topped 25 percent Tuesday in New Hampshire, a state he won with more than 60 percent of the vote in 2016. With Sanders underperforming his poll numbers, it took a sudden surge from Minnesota Sen. Amy Klobuchar, who bled votes from former South Bend, Indiana, Mayor Pete Buttigieg, to preserve Sanders' victory.

That's winning ugly.

It's not clear that he can afford to muddle along with roughly a quarter of the vote — about what he got in Iowa, too — if the field of Democrats narrows much, because that would leave him in the position of trying to muscle his way to the nomination without a majority or a large plurality of delegates.

That reality leaves Sanders with two basic paths: vastly expand the share of Democrats who prefer him — whether candidates drop out or not — or rely on the field of competitors to remain so large and so evenly matched that he can emerge as the clear light heavyweight in a class of middleweights.

Neither option is easy, and neither is fully in his control.

The unique challenge for him is that he has shown little ability to attract support from other corners of the party. Voters who back faltering candidates appear to be shifting significantly between contenders — but not shifting to Sanders.

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It's a dynamic that bodes poorly for him in either an extended primary season with a streamlined field, or in a brokered convention situation.

"It's simple math," Nomiki Konst, who served as a surrogate for Sanders in his 2016 presidential campaign, said in a text exchange with NBC News. "The more candidates, the more the vote splits. None of the other candidates have the juice to get through Super Tuesday — except Bernie and, sadly, Bloomberg. You get a movement or an oligarch. Pick a side now. None of the other candidates have a shot."

Sanders' campaign manager, Faiz Shakir, told MSNBC's Stephanie Ruhle on Friday that he doesn't see a two-man race right now. Instead, he's looking for his candidate to dominate a full field that remains at parity for some time.

"I think that there's going to be at least four or five, six candidates right at the top," Shakir said. "You don't hear me thinking or believing that this is somehow a two-man race."

Sanders himself has begun to frame the argument, with a little wiggle room, that the nominee should be whoever has accumulated the most delegates by the time all the states have voted. He told MSNBC's Chris Hayes on Wednesday that it would fracture the party if a candidate who finished first did not win the nomination — even if that candidate only collected a plurality of delegates because more than two competitors collected enough delegates to prevent anyone from attaining a majority.

"In general, I think it is a fair statement to say that it would be very divisive," Sanders said. "The convention would have to explain to the American people, 'Hey, Candidate X got the most votes and won the most delegates at the primary process, but we're not going to give him or her the nomination.' I think that would be a divisive moment for the Democratic Party.”

Nearly every Democrat has a two-part theory about how Sanders' winning a plurality of delegates could play out: The first part is that it would be hard for the party to stop him from taking the nomination if he had a large plurality — more than 40 percent and far larger than his closest competitor — and that there is some undetermined lower threshold at which his claim to the nomination would become less powerful. Whatever the case, it's hard for Sanders, his supporters or his critics to predict the sentiments of the delegates, voters and party elites in advance of an actual outcome.

Konst's construct is telling because it favors a two-candidate race — and because it envisions Sanders and Mike Bloomberg, the former New York mayor, as those candidates.

There are reasons to think Bloomberg will be competitive, but he has hardly dispatched with the rest of the field at this point. He hasn't appeared in a debate or on a ballot yet, and he is polling third in national surveys. But Sanders' best shot at winning the nomination may now rest on the billionaire businessman-turned-politician wiping out the rest of the candidates between himself and Sanders on the ideological spectrum.

That would give Sanders an opportunity to fight for the votes of Democrats who currently prefer other candidates but might not love the idea of turning the party over to Bloomberg, a chance to expand a base that right now looks to be locked in place.

The contrast between the populist progressive Sanders, who has rejected the Democratic Party label because of his distaste for the establishment's ties to corporate power and campaign money, and the alpha capitalist, former Republican Bloomberg is unambiguous on economic matters. Sanders would love nothing more than to run his campaign solely against Bloomberg and Trump, a pair of fabulously wealthy New Yorkers, on the David-vs.-Goliath message that has been the hallmark of his political profile for decades.

The fact that Bloomberg and Sanders agree on most of the bedrock domestic social issues — abortion, gun control and others — would leave them room to duke it out on the economy. But there are other candidates in the race who have no intention of ceding their support to Bloomberg or Sanders. And most of them believe there's a path to the nomination that can be secured by becoming the one true alternative to Sanders and Bloomberg.

That basically means portraying Sanders and Bloomberg both as extremes who don't reflect the mainstream of the Democratic Party. The middle spot has been a thresher so far for primary candidates who have risen to prominence between the centrist and progressive poles of the party. Now, there are only a handful remaining.

The silver lining of Sanders' dark cloud is that all the other candidates also have obstacle-filled paths to the nomination.

The worst-case scenarios for Sanders involve a two-or-three-candidate race in which his number doesn't grow much from the 25 percent level, or one in which a larger field of candidates bleeds delegates from him rather than his main competitors. Following a week in which Sanders saw the vast majority of late-deciding voters sign up with his rivals in New Hampshire — and some early deciders shift from one of his rivals to another — his margin for error looks narrow.

Then again, Shakir, his campaign manager, gained a measure of fame at Harvard for delivering clutch hits like the bases-loaded single he knocked as a freshman to secure an Ivy League title and an ugly blooper he misdirected to get the Crimson into a championship game as a senior.

"It was garbage," Shakir said then of that second hit. Garbage wins, like the Klobuchar-aided triumph in New Hampshire, are better than losses for Sanders. But, as Shakir said when he was in college, bigger margins are ideal. “I hope we win by 10 or something."

On Friday, he said he was happy that Sanders increased his total of the popular vote from 24.7 percent in Iowa to 25.7 percent in New Hampshire.

"We keep raising the roof, right?" he said. " Every time we raise the bar and win more support sometimes, you know, we hear from other critics, ‘well, it’s not big enough.’ From my perspective, you win Iowa and New Hampshire [by popular votes], that's a good outcome."

Good, sure — but not quite the same as being on track to win the nomination.