WASHINGTON (AFP) - Donald Trump's triumphal march toward the Republican presidential nomination left his party in disarray on Wednesday as Democrats coalesced around their White House frontrunner Hillary Clinton after her slew of Super Tuesday victories.
Both candidates emerged the clear winners after party nominating contests in a dozen states, piling up delegates on the biggest, most pivotal day of primaries in the race to replace President Barack Obama.
Trump was victorious in seven of 11 states, weakening but not eliminating his rivals, while Clinton equalled that score with wins in seven states against Bernie Sanders, absorbing a formidable challenge from the left.
But whereas Clinton appeared to solidify her support ahead of the next key round of primaries on March 15, divisions within the Republicans deepened over Trump's success with a slashing campaign that has galvanised disaffected voters but opened wounds on racial, ethnic and gender fronts.
With the 69-year-old billionaire powering past their favoured candidates, Republican stalwarts have raised the possibility of the party splintering if Trump wins the nomination.
"I think that's a very real possibility," Christine Todd Whitman, a former New Jersey governor, told National Public Radio.
"There are a lot of people who just cannot see themselves supporting Trump. You have Mitch McConnell, the Senate majority leader, telling Senate candidates if this is a problem for you, go ahead and run ads against him even if he is your party's presidential nominee."
Senator Ted Cruz and Senator Marco Rubio have both pitched their campaigns to Republican voters looking to stop Trump.
In Tuesday's polls, Cruz won his delegate-rich home state of Texas and neighbouring Oklahoma as well as Alaska, a better performance than Rubio who notched just one victory in caucuses in Minnesota.
Those wins were enough to keep them both in the race for now, but did little to quiet the alarm among their establishment backers, who fear the party is headed toward an annihilating defeat in the general elections.
"Happiness for Donald Trump is a divided opposition. He's got precisely that and it's going nowhere for the time being," said Sabato's Crystal Ball, a political newsletter published by the University of Virginia.
Trump's wins were widespread, from Alabama and Georgia in the deep south, to Massachusetts in the north-east, to the vital battleground state of Virginia.
In his victory speech on Tuesday night, the real estate mogul and reality TV star set aside his usual boastfulness to offer an olive branch to party leaders.
"I think we'll be more inclusive and more unified. I think we'll be a much bigger party," Trump said.
But Cruz used his victories to argue he is the only Republican who can beat Trump.
"For the candidates who have not yet won a state, who have not racked up significant delegates, I ask you to prayerfully consider our coming together, uniting," he said.
After his disappointing performance, Rubio ended the day in Florida - a clear signal that he is banking on a win in his home state, which votes on March 15, the next major date in the primary cycle.
Two other Republican candidates - Ohio Governor John Kasich and retired neurosurgeon Ben Carson - came up empty handed on Super Tuesday. Kasich also was expected to hang in until Ohio votes March 15.
Once a contender, Carson has faded into irrelevance.
"Republicans are reaping the whirlwind right now, and Democrats should seize the chance to show Americans an alternative to Mr Trump's politics of rage, and an image of themselves to be proud of, not shrink from," the liberal New York Times observed.
In her victory speech, Hillary Clinton signalled she is now turning her attention to a general election face-off with Trump.
"It's clear tonight that the stakes in this election have never been higher, and the rhetoric we're hearing on the other side has never been lower."
Attacking Trump's pledge to "make America great again," she said, "America never stopped being great!"
Trump painted Clinton - the former first lady, senator and secretary of state - as a Washington insider who cannot address a furious electorate's desire for change.
"She's been there for so long. I mean if she hasn't straightened it out by now, she's not going to straighten it out in the next four years," he said.
A recent CNN/ORC poll found that both Clinton and Sanders would easily defeat Trump if the general election - set for Nov 8 - were held now.
Sanders, a self-styled democratic socialist, has vowed to press on with his well-funded grass-roots campaign that has made the growing gap between rich and poor the central issue of the Democratic contest.
Sanders notched wins in his tiny home state of Vermont, Oklahoma, Colorado and in Minnesota.
But Clinton, who was unbeatable in the southern states with big African-American majorities, trounced him in Alabama, Arkansas, Georgia, Tennessee, Virginia, Texas and Massachusetts.