Super Tuesday: What happens next?
Mitt Romney won six out of 10 primaries on Super Tuesday but failed to land a knockout blow. How much longer can the Republican race go on? And what is it doing to the party's chances of beating President Barack Obama in November?
Ryan Lizza, Washington correspondentfor the New Yorker magazine, believes the drawn-out and increasingly personal primary contest has exposed deep divisions at the heart of the Republican Party.
"Some of the experts who have crunched the numbers say it is basically impossible for Santorum or Gingrich to get a majority of the delegates," after Tuesday night, he told the BBC.
However he may do well enough to prevent Romney from claiming the crown by right, and the "media narrative" is that Santorum has the momentum.
That is due in part, Lizza told the BBC's World News America, to the fact that Mr Santorum's three victories - in Tennessee, Oklahoma and North Dakota - came relatively early in the night.
Mr Romney won the crucial swing state of Ohio, but the result went right down to the wire and was not confirmed until the early hours.
Even the US TV networks, normally so quick to call election results, were unable to separate Mr Romney and Mr Santorum, who was frequently ahead during prime-time.
"The way it has played out on TV has been terrible for Romney," Lizza told the BBC.
But, more worryingly for the Republicans, is that the analysis of the voting in the 10 Super Tuesday states reveals the vote is split between the two men on religious and class grounds.
"On the religious side, evangelical Republicans, evangelical conservatives, have withheld their support for this Mormon candidate and that is a very serious issue and one Romney has not been able to overcome.
"On the class divide, as you go up the class ladder, Romney does very well. As you go down, Santorum does very well. Both of these things suggest some trouble in the fall.
"Running against Barack Obama could be enough to bring back both evangelicals and low income Republicans into the Romney fold.
"But as this race goes on, if these fissures continue, and the race gets more personal between Santorum backers and Romney backers, we could see it get worse."
'Rushing to the right'
Some drawn-out nomination battles, such as the 2008 Democratic race between Hillary Clinton and Barack Obama, can have the effect of strengthening a party, argues Ryan Lizza. But not this one.
The way that the candidates have been "rushing to the right" on social issues and immigration risks alienating many voters, particularly women and Hispanics, he says.
The second group is particularly important to the future of the Republican party.
"The [Republican] base of older whites is not growing it is shrinking - and most Republican strategists know that the future for them lies in the Latino vote.
"This primary, the past couple of years of Republican politics, have set back a lot of hard work that Bush administration tried to do in courting Latino leaders, in courting Latino voters.
"And the poll numbers right now among Latino voters, who are the future of their party, are very, very weak.
"So on a couple of key demographics that the Republican party needs if they are going to survive, these primaries have not been good for them."
After Super Tuesday, Mr Romney leads the race for the nomination with 415 delegates committed to backing him at the national Republican convention in August.
A candidate needs 1,144 delegates to win the party's nomination and go on to challenge Barack Obama in November's election.
'Good for Obama'
"Some of the experts who have crunched the numbers say it is basically impossible for Santorum or Gingrich to get a majority of the delegates after [Tuesday] tonight," said Lizza.
"They can stay in the race, and win delegates here and there, and they can prevent Romney getting a majority.
"But as of tomorrow what I think you are going to start seeing is a lot of angst from the Republicans, who are asking themselves 'why can't Romney put this race away?'"
Primaries next Tuesday in Alabama and Mississippi will play to Rick Santorum's strengths, in that they contain a lot of evangelical conservatives and low income voters. and as a result are likely to be "disastrous" for Romney, argues Lizza.
Which will be welcome news at the White House.
"This whole primary season has been good for Barack Obama.
"I think if he wins this election in the fall, we will look back at February and March as the point where it turned around, with Republicans fighting each other and moving to the right, while Obama was improving his poll standing and the economy was improving."