Donald Trump as the front-runner for the nomination, with his two leading rivals. (File Photo)

South Carolina's Republican primary has often had a truly clarifying effect on the party's presidential nomination race. Saturday's results appeared to fall short of fulfilling that role.At a minimum, the outcome here solidified New York businessman Donald Trump as the front-runner for the nomination, with his two leading rivals now Sen. Ted Cruz of Texas and Sen. Marco Rubio of Florida, who were in a dogfight for second place.In other important ways, however, the voters here kicked the contest on to the next round of states without resolving some of the most critical - and interrelated - questions about the direction of the GOP race.At the top of the list of questions is the degree to which Trump has a ceiling on his support that could eventually deny him the nomination, despite having finished second, first and first in the first three contests of 2016. Trump's winning percentage was the lowest or second lowest recorded here over the past 10 presidential primaries.Another is the issue of whether Cruz, who needed South Carolina to give him a substantial boost, can use his finish here as a springboard to victories in the Southern states on March 1 that long have been the foundation of his victory plan. Related is whether he can only score well in states where the electorate includes an overwhelming percentage of evangelicals.Finally, there is the biggest question, which is whether Rubio can isolate and then defeat Trump in an eventual one-on-one showdown for the nomination. Rubio's finish here provided a lift to his candidacy after his disappointing fifth-place finish in New Hampshire, but as long as the race remains a three-person contest, Rubio's path is made more difficult.Trump's victory continues the story of his remarkable candidacy, which has shaken up the Republican Party on the strength of his anti-immigration, anti-trade, anti-establishment message. Only once since 1980 has the winner of the Republican primary here not gone on to win the nomination. The exception was four years ago, when former House speaker Newt Gingrich carried the state.Trump's victory came after a tumultuous week in which he first accused former president George W. Bush of lying about the existence of weapons of mass destruction as the pretext for invading Iraq and later landed in a verbal spat with Pope Francis, who had labeled Trump's views on immigration un-Christian.How much that hurt him wasn't entirely clear from the exit polls.One imperfect measure is where late-deciding voters ended up.Trump had a margin of nearly 2 to 1 among the 60 percent of voters who said they had made up their minds before the last few days of the primary. Among the other 40 percent, however, he ran third behind his two leading rivals.As the campaign moves soon from a series of isolated contests in single states to primary days with multiple contests across a much wider terrain, Trump holds some key advantages.The principal one is that the race will become ever more nationalized, favoring someone who has shown mastery in dominating media coverage at the expense of his rivals.A second is that his coalition appears similar to that of past winners of the nomination, as he is doing better than the others among Republicans who call themselves "somewhat conservative" or "moderate," rather than those who say they are "very conservative."A third is that against a divided opposition, Trump can continue to win primaries and caucuses with less than half the vote. That could become significantly more valuable starting on March 15, when states award delegates on some version of a winner-take-all basis.Were Trump a traditional candidate, he would be seen as an even stronger front-runner. But because he continues to go against many tenets of modern conservatism, he remains suspect to many in the party.Exit polls showed some potential cracks in Trump's facade. He scored overwhelmingly among voters looking for someone who tells it like it is and led the field among those who are looking for a candidate to bring change to Washington. But among those in South Carolina who said that they wanted a candidate who shares their values, just fewer than 1 in 10 backed Trump. And for those who put electability at the top of their list of priorities, Rubio was the clear winner, with Trump and Cruz well behind.The faster the race narrows to two candidates, the greater the hope among the anti-Trump Republicans that they can stop him. But whether Cruz or Rubio could emerge to play that role was up in the air after Saturday's results.Cruz's advisers long have argued that he is best positioned to be the alternative, and he has attempted to position himself as the most pure conservative in the field. South Carolina's electorate, wherein 8 in 10 voters called themselves conservative and more than 7 in 10 identified as evangelical Christians, seemed ideally suited to his candidacy.Instead, he not only fell short of victory, he was in danger of ending up in third behind Rubio. Remarkably, the candidate who has done more to position himself as the candidate for evangelical Christians was narrowly losing the evangelical vote. A few weeks ago in Iowa, he beat Trump and Rubio among evangelicals, each by double digits.Trump's appeal to working-class voters spilled into the competition for the vote of evangelicals. Among evangelicals without college degrees, Trump led Cruz in South Carolina by low double digits and led Rubio by nearly 3 to 1. Among those with college degrees, the three candidates were closely bunched, with Rubio leading through much of the evening.Cruz, like Trump, taps some of the same anger with the establishment among grass-roots Republicans. He would be helped if Ben Carson pulled out of the race, as they have potential overlap in their support base. Absent that, he must find a way to invigorate the coalition he envisioned when he set out his strategy to overtake Trump.His advisers think that, if he can, the race will eventually winnow to Trump vs. Cruz. For Cruz, March 1 has been transformed from a day when he stamps himself as front-runner to a day he must use to make himself the principal alternative to the reality TV star.Rubio's strategy remains as it has been for some time - survival through early contests and supremacy late in the primary-caucus season. He had some major advantages in South Carolina, with endorsements from the rising generation of Republicans here in Gov. Nikki Haley, Sen. Tim Scott and Rep. Trey Gowdy.Rubio also showed that his faltering performance in the New Hampshire debate was not a fatal misstep. He moved up in the final week of campaigning to take on Cruz for second.The best news for Rubio is that former Florida governor Jeb Bush's disappointing finish brought a swift conclusion to a campaign that was knocked off stride by Trump's entry into the race and that never again found its footing. It was an ironic end that his candidacy foundered in a state that solidified his father's front-running candidacy in 1988 and helped save his brother's candidacy in 2000.Rubio needs voters in the establishment wing to coalesce as quickly as possible around his candidacy, and Bush's absence could accelerate that process. But for now, that is complicated by the persistence of Ohio Gov. John Kasich as an active candidate.Having played down the importance of South Carolina to his campaign, Kasich will seek to survive for two more weeks, but he faces an extremely challenging road ahead. He carries a unique message in the GOP race, that of a pragmatic conservative who favors working with Democrats at a time when many Republicans favor confrontation.Kasich has staked his future on the state of Michigan, whose primary does not take place until March 8. To survive until then, however, he will have to weather 16 earlier contests, with more than 750 delegates at stake. The more he finishes behind the three leaders across a swath of states before Michigan, the more difficult that will become.Trump proved again that he is the dominant force in the GOP race, for now. But the outcome here foreshadows a ferocious struggle ahead, for the candidates and the party they seek to lead.© 2016 The Washington Post