Republican US presidential candidate Donald Trump waves to supporters at a Super Tuesday campaign rally in Louisville, Kentucky March 1, 2016.[Photo/Agencies]

'DONALD TRUMPS OF THE WORLD'

Sanders thanked cheering supporters in his hometown of Burlington, Vermont, and assailed the Republican front-runner.

"We are not going to let the Donald Trumps of the world divide us," said Sanders, 74, adding that he expected to pile up "hundreds" of convention delegates in voting on Tuesday.

For Rubio, 44, it was a day of reckoning. His losses piled up after a week in which he labeled Trump a "con artist" and exchanged schoolyard taunts with him over, for example, who wet their pants under pressure at a debate last week.

Suddenly, the contest on March 15 in Florida, his home state, loomed over him as a must-win state.

"Florida, I know you're ready," Rubio said. "The pundits say we're underdogs, I'll accept that. We've all been underdogs."

Rubio's plight was such that Senator Lindsey Graham, an establishment South Carolina Republican, told CBS News that Republican voters might need to rally around Cruz, who has been one of the most disliked public figures in Washington.

"I can't believe I would say yes, but yes," Graham said when asked about the idea of supporting Cruz as a way of stopping Trump.

Cruz told supporters at his victory party in Texas that Trump was a "Washington dealmaker, profane and vulgar, who has a lifelong pattern of using government power for personal gain."

The networks had yet to project a winner for Republicans in Alaska.