Washington - Donald Trump's triumphal march towards 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 on Tuesday after several party nominating contests, piling up delegates on the biggest, most pivotal day of primaries in the race to succeed President Barack Obama.
Trump was victorious in seven of 11 states, weakening but not eliminating his top rivals Ted Cruz and Marco Rubio, both US senators.
Retired neurosurgeon Ben Carson meanwhile announced after his poor Super Tuesday showing that he did not "see a political path forward" in the race.
Carson's campaign soared last year but steadily lost steam amid questions over his personal narrative and lackluster debate performances.
Should Carson officially drop out, that would leave Trump and a trio of pursuers: Cruz, Rubio and Ohio Governor John Kasich.
Clinton equaled Trump's score with wins in seven states against Senator 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 March 15, divisions among Republicans deepened over Trump's success with a slashing campaign that has galvanized 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." Cruz and 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 Minnesota.
Those wins 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," according to 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 northeast, to the vital battleground state of Virginia.
In his victory speech Tuesday, 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.
Hours later, the sweet nothings evaporated.
"Marco Rubio lost big last night. I even beat him in Virginia, where he spent so much time and money," Trump posted to his 6.5 million Twitter followers Wednesday.
"Now his bosses are desperate and angry!" 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 - before Rubio notched his Minnesota win.
After his disappointing performance, Rubio ended the day in Florida - a signal he is banking on a win in his home state, which votes on March 15, the next major date in the primary cycle.
"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 New York Times observed.
In her victory speech, Clinton signaled 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," she said.
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 November 8 election were held now.
Sanders, a self-styled democratic socialist, has vowed to press on with his well-funded campaign that has made shrinking the gap between rich and poor a central issue of the Democratic contest.
Sanders notched wins in his home state of Vermont, Oklahoma, Colorado and Minnesota.
Clinton, buoyed by overwhelming African-American support, trounced him in Alabama, Arkansas, Georgia, Massachusetts, Tennessee, Texas and Virginia.