Paul Tully was a burly, chain-smoking, hard-drinking Irishman from Long Island – and one of the best presidential campaign operatives I’ve ever met. He had been a football lineman at Yale, gotten a law degree at Penn and been a labor organizer in Philly. He was part dock worker, part professor.

We were having a drink at a bar on Milk Street in Boston one afternoon years ago when he explained campaigns to me in a way I never forgot – and it is my guide to the Democratic presidential race on the eve of Super Tuesday.

“There are no straight-line extrapolations in campaigns,” he said. “They are a curved, interactive universe. You can’t use a ruler. You start at one point here and end up over there at some other point you could not have expected.”

And that is why there are more questions than answers right now. Here are four:

HOW DID JOE BIDEN RE-EMERGE?

His revival proves the Tully Theorem. Yes, his team had planned all along for South Carolina to be his “firewall,” but the state would have been his firetrap instead had it not been for an unforeseeable chain of circumstances – and some uncharacteristic good luck.

Essentially, he should thank … Elizabeth Warren.

Bernie Sanders’ swift rise scared House Democratic leaders into a frantic search for a unifying moderate. That might have been Mike Bloomberg, but Warren devastated him in two television debates, which galvanized South Carolina Rep. Jim Clyburn. A key member of Speaker Nancy Pelosi’s inner circle and a Moses-like political figure in the Palmetto State, he endorsed Biden, rallying black voters behind him.

It also helped Biden that African-American candidates flamed out early and that Bloomberg, who also has been courting that vote, chose not to compete there. Lesser-billionaire Tom Steyer did so, and bombed.

Sanders helped late by visibly and vehemently defending “democratic socialist” policies, which are anathema to South Carolina voters, black or white. The civil rights generation saw segregationists try to discredit Martin Luther King and his colleagues as ideological insurrections and don’t want to see a repeat.  

IS BIDEN NOW GOING TO DERAIL BERNIE?

The Tully Theorem says, “Not clear.” Again, you can’t use a ruler and draw a line to the 1,991 delegates he (or Bernie) needs for the nomination. Especially not in Biden’s case. Biden’s all-or-nothing play in South Carolina – he had no choice – has yielded a spurt of cash and that ineffable thing called “momentum.” But the foreshortened primary calendar left him without time to organize and advertise in the 14 states that hold primaries tomorrow. In most of them, Sanders is leading and in line to pick up huge chunks of the delegates.

The width and depth of the Sanders grassroots organizations in those states is impressive. With a history going back to his national effort in 2016, it is unrivaled. The former vice president will have to pick his spots – Southern states with substantial black populations, for example – but the goal is tactical survival rather than a sweep.

Perhaps the most important thing South Carolina did for Biden was restore his confidence and sunny disposition. It renewed his sense of mission. He also found a theme: He’s a real Democrat; Sanders and Bloomberg aren’t.

WHAT ABOUT BLOOMBERG?

One of his top advisers told me at launch in November that they would finish Super Tuesday with the delegate lead, and then cruise on to the nomination. They were confident, even cocky, about Bloomberg’s ability to carpet-bomb his way to an overwhelming position in giant states such as California and Texas, which have so many expensive media markets that no other candidate could come close to saturating them the way he could.

“No campaign has been able to even attempt anything like what we are going to do,” the aide said.

All of that is true – the scale is massive – but things haven’t gone as planned. Warren happened. The former New York mayor’s other live appearances have been underwhelming. Bernie rose more rapidly than anyone anticipated, which created a compelling story that dominated the news.

Bloomberg will be lucky to come out of Super Tuesday in third place.

What then? As New York-based political analyst John P. Ellis, a close student of Bloomberg’s, points out, the candidate’s business mantra is “In God we trust. Everyone else bring data.” The spreadsheets may not look promising come Wednesday and if Bloomberg is going to be seen as the guy who got Sanders the nomination – by dividing the moderate vote -- he will consider dropping out.

WILL THERE BE A “BROKERED” CONVENTION?

Suddenly, it’s 1952! Everyone, including me, is reading up on the last truly contested Democratic political convention, in Chicago. None of the main contenders arrived in the Windy City with a majority, and the early leader, Sen. Estes Kefauver of Tennessee, lost on the fourth ballot to host Gov. Adlai Stevenson, who was drafted for the spot.

Sanders is very likely to have a big lead after tomorrow night, but, again, there is no straight line to the 1,991 pledged delegates needed for a first-ballot victory. The party rules give delegates to candidates who get at least 15% statewide or in congressional districts. There is no winner-take-all.

The idea was to eliminate low-vote losers, but stretch out the process for the top tier. The plot twist in 2020 is that mega-states California and Texas are voting so early that a candidate (Sanders) can get a lead but have trouble closing out the race.

That, at least, is Sen. Warren’s hope. She and her aides insist that the race is indeed going to the Milwaukee convention, and that she is in it all the way. But once again, no straight line. If she loses her home state of Massachusetts to Sanders – a distinct possibility – she could wind up in a different place.