MIAMI -- Gripped by chaos and dismay, Republican leaders searched on Wednesday for a last-chance option that could derail Donald Trump's momentum fueled by seven commanding Super Tuesday victories.

Overshadowed by Trump's wins, Ted Cruz came in a close second in the night's delegate haul, thanks to a win in his home state of Texas. The strong showing bolstered the senator's case to be the party's Trump alternative, even as rival Marco Rubio vowed to continue his fight.

The unrelenting division represents the biggest crisis for the GOP in decades, with the party seemingly on track to nominate a presidential candidate it can't control. Some party leaders are considering the once unthinkable option of aligning behind Cruz, whom many dislike, while others are talking of a brokered convention. Some influential outsiders even raise the option of forming a new party.

Though convention fights are much more talked about than actually occur, an Associated Press delegate count indicates Trump will have to do better in upcoming contests to claim the nomination for president before the party's national gathering in July. So far, he has won 46 per cent of the delegates awarded, and he would have to increase that to 52 per cent in the remaining primaries.

The GOP mayhem contrasted sharply with the increasing cohesion on the Democratic side, where Hillary Clinton locked down solid victories in seven states and was on the path to regaining her status as the inevitable nominee. Clinton's dominance with black voters carried her to wins across the South. Still, Bernie Sanders picked up wins in his home state of Vermont and in Minnesota, Oklahoma and Colorado, and he vowed to fight on.

The Democratic drama paled in comparison to the existential questions Republicans wrestled with in the wake of the most significant election night of the primary. Trump won handily in states as politically opposite as Massachusetts and Alabama, a sign of his broad, outsider appeal and energizing impact on voter turnout.

Along with Texas, Cruz took neighbouring Oklahoma and also Alaska. Florida Sen. Marco Rubio won only liberal Minnesota.

Despite Trump's commanding victories, many Republican leaders remained deeply skeptical Trump could beat Clinton in a head-to-head matchup in November -- and some questioned whether they'd want him in the White House if he did. They turned to the sort of "break glass" options once thought impossible.

"Ted Cruz is not my favourite by any means," Sen. Lindsey Graham, a former candidate whose disdain for his Texas colleague is well known, told CBS News. "But we may be in a position where rallying around Ted Cruz is the only way to stop Donald Trump and I'm not so sure that would work."

Still, Graham also cast doubt on whether elder GOP statesmen could wrest hold of the situation.

"At what point do you realize the Republican Party is unorganized -- like the Democratic Party? There's no secret group of people," he scoffed.

The comments came as .NeverTrump hashtag spread across Twitter and an anti-Trump Super Pac released a new online video and said it would increase its daily attacks ahead of primaries on March 8 and March 15. Our Principles PAC latest attack blasts Trump for not clearly repudiating David Duke, a onetime KKK member who endorsed Trump's campaign. The episode was an example of why Trump should not win the nomination, said the group's new spokesman Tim Miller, a former aide on Jeb Bush's failed campaign.

"We will fight until the last delegate is counted to stop that from happening," Miller said.

Other prominent Republicans called for more drastic measures.

"It may be necessary for men and women of principle within the party to set the self-detonation sequence as they escape the ship to a new party," wrote conservative blogger Erick Erickson. Erickson was among those calling on the party to coalesce around Cruz.

In his victory speech, Trump sent a clear message to the GOP establishment, warning to House Speaker Paul Ryan, who had declared earlier Tuesday that "this party does not prey on people's prejudices," that if the two don't get along, Ryan is "going to have to pay a big price."

Delegate math would seem to underscore the problem for Republicans who reject Trump. , as the brash billionaire businessman carried seven states and continues to barrel toward the 1,237 delegates needed to secure the GOP nomination.

For the night, Trump won at least 234 delegates and Cruz won at least 209. Marco Rubio was a distant third with at least 90. There were 595 Republican delegates at stake in 11 states. There were still 40 delegates left to be allocated Wednesday morning.

Overall, Trump leads with 316 delegates and Cruz has 226. Rubio has 106 delegates, John Kasich has 25 and Ben Carson has eight.

The math was also tough for Sanders. Clinton was assured of winning at least 457 of the 865 delegates at stake Tuesday. Sanders gains at least 286. When including party leaders, Clinton has at least 1,005 delegates and Sanders has at least 373. It takes 2,383 delegates to win the nomination.

Top Sanders advisers said Wednesday that the Vermont senator would push ahead, arguing that Super Tuesday was the best day on the primary calendar for Clinton. But the map will get more difficult for her moving forward, said Sanders senior adviser Tad Devine.