Who might stop Trump from nomination win?
With just a handful of weeks until the Iowa Caucuses, the race for the Republican presidential nomination is entering the home stretch.
Here's a look at the 12 candidates remaining in the Republican field - and their path to victory … or defeat.
Hope is lost
Jim Gilmore, Rick Santorum, Mike Huckabee
Former Virginia Governor Gilmore was too long removed from public office and too not-named-Bush to ever have a shot. Santorum and Huckabee, both former Iowa Caucus winners, have failed to recapture that old magic on the campaign trail. They've put all their eggs in a good showing in Iowa, and at this point that's just not going to happen.
How one of them wins: A giant meteor strikes the site of next Republican candidate debate.
How they lose: Already taken care of, thanks.
Running out of time
Fiorina's moment, when she shot to the top of opinion polls following a bravura performance in the second Republican debate, seems like a long time ago. In the four months since then, her fortunes have steadily diminished, as she's struggled to stay in the headlines. Fiorina has spent roughly equal time in Iowa and New Hampshire, and unless she stages a late comeback in either place, she likely won't last long after that.
How she wins: A strong showing in one of the two debates before Iowa gives her a bump that actually has staying power.
How she loses: Ignominious defeats in Iowa and New Hampshire lead to an early return to the lecture circuit.
Once upon a time, Paul was considered a top-tier candidate. Negligible standing in early state opinion polls, however, have left his campaign stuck in also-ran status. Even a heralded debate performance last month in Las Vegas appears to have done little to reverse his fortunes.
How he wins: The college-age libertarians and disaffected Republicans who fuelled his father's insurgent campaigns in 2008 and 2012 take a break from tweeting Star Wars spoilers and show up in Iowa and New Hampshire in large numbers, allowing him time to build the non-traditional Republican coalition he envisioned when he launched his campaign.
How he loses: His father's supporters opt for Ayn Rand book club meetings instead of heading to the polls, and traditional Republican voters continue to snub him.
The retired neurosurgeon still has reasonably strong poll numbers, but his trajectory has been heading straight down. Political fallout from the Paris attacks - and the subsequent renewed focus on strong leadership skills and foreign policy acumen - have left the sedate candidate in a tenuous position. A mass exodus of top staff just before New Year gave further support to the view that the Carson campaign is a sinking ship.
How he wins: Evangelicals in Iowa who fuelled his rise return to the fold, leading a top-two finish there and renewed interest in his candidacy.
How he loses: The nosedive continues, and like grains of wheat through a pyramid, so go the days of Carson's campaign.
He's got the money, but will he ever find the love? Although the former Florida governor is looking a bit more solid on the campaign trail, it may be too little, too late at this point. New Hampshire saved his father's campaign in 1988, and it may be Jeb's last hope. While he has the infrastructure to battle on after that, establishment and moderate Republicans will likely have found another candidate to rally behind by then.
How he wins: A strong showing in New Hampshire keeps his head above water, allowing his greater financial resources to come into play as the campaign grinds on for months.
How he loses: He's a non-factor in Iowa, and he finishes behind his establishment competitors in New Hampshire. His father's old advisers take him aside and gently explain that it's time to find another life goal.
The Ohio governor has put all his eggs in the New Hampshire basket, but after a surge there early in the autumn he's now polling roughly at parity with all the establishment candidates in the high single digits. If he can break through and beat Bush, Marco Rubio and Chris Christie, he could make a move. If not, it's likely curtains for the governor.
How he wins: A top-two finish in New Hampshire helps anoint him as the sensible man to beat Cruz or Trump.
How he loses: New Hampshire proves to be his Waterloo.
The New Jersey governor is in a similar position to Kasich, pinning his hopes on New Hampshire, but his outlook is slightly better because he's been steadily improving his numbers while the Ohio governor has stagnated. He also has surprising institutional support in Iowa, including the backing of key aides to Governor Terry Branstad. That hasn't translated into any momentum yet, but Christie has started spending more time in the Hawkeye State.
How he wins: A solid third-place finish in either Iowa or New Hampshire will give his campaign life.
How he loses: Blowout losses in the first two contests or an inability to translate successes there into more national appeal sends him back to New Jersey.
With consistently strong debate performances and a slow-but-steady approach to campaigning, many expected Marco Rubio to emerge as the man to challenge Trump and the other anti-establishment outsiders. That just hasn't happened yet. He's well behind Trump and Cruz in Iowa and mired in a slugfest with the other mainstream candidates in New Hampshire. His super PAC recently launched a negative ad blitz against Christie, which is a surprising demonstration of concern about a candidate he should be easily outperforming by now.
How he wins: A strong showing in Iowa or New Hampshire solidifies the support for traditional Republican voters and allows him to persevere until Florida and more moderate states give him wins in mid-March and thereafter.
How he loses: He's yet to make a move in any state - and maybe he never does. He ends up the candidate everyone sort-of likes but nobody votes for.
The Texas senator finds himself in an enviable position. If Trump fades, he inherits the New Yorker's disaffected supporters. If Trump endures, he could become the only viable alternative to a panicked Republican establishment. Not bad for a candidate the New York Times derided as having a slim to no chance of winning when he entered the race in March.
How he wins: As is now expected he is victorious in Iowa, allowing to him to survive a loss in New Hampshire. Then he racks up win after win in the Southern primaries that follow. By the time an establishment candidate emerges to challenge him, he has an insurmountable lead.
How he loses: A surprise defeat in Iowa will kill his momentum. Trump could become an unstoppable juggernaut after winning New Hampshire, or an establishment candidate emerges there who consolidates support, while Cruz and Trump divide outsider votes.
It's January, and Trump is still going strong. While he's been eclipsed by Cruz in Iowa, New Hampshire looks good for the billionaire. He's drawing huge crowds at rallies across the country, including in South Carolina and other key states in the South. Now he's spending millions on television advertising. The man is in this for the long haul.
How he wins: Beating Cruz in Iowa would be a significant boost. Otherwise, he holds onto New Hampshire, wins in South Carolina and steamrolls into the Southern primaries in March. Clint Eastwood nods approvingly as Trump delivers the first-ever ad-libbed acceptance speech at the Republican National Convention.
How he loses: Trump supporters, many new to the political process, never find their way to the voting booth. He suffers a resounding defeat in Iowa, damaging his self-styled proven-winner identity. Either he loses New Hampshire, which seals his fate, or he wins, but the party establishment rallies around a candidate to stop him. He delivers an epic withdrawal speech that insults every Republican candidate, Rosie O'Donnell, Samuel L Jackson, anyone who didn't vote for him and the entire population of Mexico.
Republican candidates in, and out, of the 2016 presidential race