NORTH CHARLESTON, S.C. - Eighteen days before the Iowa caucuses, the Republican nomination contest has come down to two big questions: Can Donald Trump actually become the party's 2016 presidential nominee, and if he falters, who can emerge to seize the crown?
What was unthinkable a few months ago no longer is. Trump's durability in national polls and his standing in the early states have forced GOP leaders - and all his rivals - to confront the possibility that the New York billionaire and reality TV star could end up leading the party into the fall campaign against the Democrats.
Trump is anything but a typical front-runner. In fact, he is the most unconventional and atypical front-runner for as long as anyone can remember. And unless and until he actually wins primaries and caucuses, the race will remain what it has been for months: a confusing mash-up among a relative handful of candidates looking to pick up the pieces of a possible Trump breakdown.
Almost everything about Thursday's debate here in South Carolina underscored the current state of the campaign. It featured a series of sharp exchanges between Trump and Sen. Ted Cruz of Texas and efforts by the other candidates to break through by showing they could be tougher on President Obama than any of their rivals.
The GOP race is now commonly defined as a pair of contests. The first features Trump and Cruz fighting to emerge as the leading candidate in what is either defined as the anger lane, the populist conservative lane or the outsider lane. In their own ways, both Trump and Cruz embody the vibrant anti-establishment anger of the grass roots.
The other contest is the battle among more mainstream conservatives, representatives in one form or another of a nervous party establishment worried about protecting down-ballot candidates in the fall.
That battle features Sen. Marco Rubio of Florida, New Jersey Gov. Chris Christie, Ohio Gov. John Kasich and former Florida governor Jeb Bush. Normally, the establishment is in the driver's seat in nomination battles. This time, those candidates have found themselves on the defensive and struggling to adapt to a Trump-dominated environment.
But nothing is quite as clean as all that. Trump occupies space largely defined by his unique candidacy. He is not a pure conservative in any sense of the word. Although his and Cruz's support overlap, Trump is in a lane of his own. It remains to be seen whether his support is wide, deep and loyal or shallow and fickle in the face of any signs of weakness.
Attacks are now flying in all directions, as the debate demonstrated. Cruz and Trump, who spent most of last year playing nice to each other, traded blows over whether Cruz, born in Canada to an American mother, is eligible to be president and over whether the values of New York are out of touch with those of the rest of the country. Cruz scored points on the first, while Trump effectively countered the second with a paean to New York's collective response to the attacks of Sept. 11, 2001.
Because there is no dominant figure among the tightly bunched establishment candidates, they are all firing at one another. Bush and his well-funded super PAC have been the most aggressive of late, but Christie, Rubio and Kasich are using what resources they have - whether through advertising and direct mail or TV and print interviews - to launch their own assaults.
Thursday's debate, however, highlighted the current plight of the establishment candidates. Overshadowed by the exchanges of Trump and Cruz, they struggled to stand out in the crowd. Christie and Rubio traded harsh words at one point, and Bush sought several times to undermine Trump. All tried to use their time to attack Obama. But no one seemed to gain much ground against the others.
The other reality of the campaign is that it is playing out separately in Iowa and New Hampshire. In Iowa, Trump and Cruz are the clear leaders. A few weeks ago, Cruz held a double-digit lead in a Des Moines Register-Bloomberg Politics poll. This week, that same poll showed his lead over Trump down to three percentage points.
Given polls that show Trump well ahead in New Hampshire, the outcome in Iowa has huge implications. A Trump victory in Iowa would send seismic shocks through the party. No Republican in the modern era has won both the Iowa caucuses and the New Hampshire primary. Trump would be in a position to do so.
A Cruz victory in Iowa, however, would rattle the establishment almost as much as a Trump victory, if not more. Unique among the elected and former elected officials in the race, Cruz campaigned from the start with an eye toward tapping anti-Washington sentiment among party conservatives. Party leaders fear that Cruz as the nominee could bring about a landslide loss in November. Cruz, who has played the campaign as smartly as anyone to date, is determined to disprove the doubters.
The establishment battle takes place primarily in New Hampshire, where Rubio, Christie, Kasich and Bush are seeking to emerge as the candidate with the momentum to carry the fight well into the spring. Right now, however, that battle is for second place. Not since then-governor Bill Clinton came in second in New Hampshire and declared himself the "comeback kid" has runner-up offered as many rewards as in this year's GOP race.
But there are other crosscurrents shaping the race. As much as the Trump-Cruz contest defines the Iowa race, the battle for third place there also has real implications. Rubio currently holds third place in the Register-Bloomberg poll, but Ben Carson, who once led in the state, is just a point behind.
None of the other candidates, with the possible exception of Trump, wants to see Rubio as the clear third-place finisher in Iowa. Establishment candidates know that if Rubio takes third there over the rest of them, he will have momentum heading toward the New Hampshire primary eight days later.
But Cruz, too, wants to hold down Rubio in Iowa; Cruz senses that the fellow first-term senator represents a major threat if he is not stopped early. Belying the idea that the race is running in two separate lanes, Cruz's super PAC took aim at the Florida senator with a new television ad attacking Rubio for having supported comprehensive immigration reform, including a pathway to citizenship for those who are here illegally.
Their competition erupted in the final minutes of Thursday's debate in an angry exchange between the two that highlighted the distrust now existing between them.
Trump has absorbed fewer attacks to date. That's partly because those who have attacked him have generally paid a far higher price than he has. But another reason others have left him alone is because they still believe he will be far more vulnerable when the field is winnowed by the results in the early states.
That is based on evidence that, however passionate Trump's supporters may be, there is a large block of voters in the party who tell pollsters they will never back him. Were he to win Iowa and New Hampshire, however, everyone's calculations about his strength and staying power would change - and he would find himself under far more intense and sustained attacks heading into the next rounds of contests.
Republicans still could be heading for something they've seen before: a contest that pits a mainstream, establishment candidate against a conservative backed by the party's social and religious conservatives.
Or it could be a race pitting Trump and Cruz, with establishment candidates destroying one another in the battle for supremacy, the ultimate evidence that the balance of power in the Republican Party has now tipped in favor of the anti-establishment grass roots.
Or the party could be heading for something it's never had in modern times: a true three-way contest that includes Trump, Cruz and someone else from the establishment wing - a race that could cause chaos and division far into the spring.
Answering the question of whither Trump is the first key to knowing which it will be.