The Fix's Aaron Blake sets up the stakes for Republican and Democratic presidential candidates on Super Tuesday. (Peter Stevenson/The Washington Post)

The Republican presidential hopefuls darted throughout the South and New England on Monday on a frantic sprint before a fateful Super Tuesday, when voting in nearly a dozen states could help determine if anyone has a chance to stop Donald Trump as the runaway leader for the nomination.

Ahead of the single biggest delegate haul yet, Ted Cruz pleaded with voters in his home state of Texas for their support — banking on a primary victory here Tuesday to give him bragging rights and to jump-start his sputtering candidacy.

Marco Rubio, meanwhile, sought to unite the GOP’s anti-Trump forces under his own banner as he addressed swelling crowds in suburban areas.

Both visibly fatigued from weeks of breakneck travel, Cruz and Rubio campaigned Monday as if they were cramming for an exam. The senators volleyed stinging character attacks at Trump, one after another, in a desperate move to halt the billionaire mogul’s momentum.

But if the polls and roaring crowds that greeted Trump in Virginia and Georgia on Monday were any indication, he is steamrolling toward a triumphant showing Tuesday. Primaries or caucuses will take place in 11 states — seven across the South, as well as Alaska, Minnesota, Massachusetts and Vermont — and the only one Trump is not expected to win is Texas, where Cruz appears to be the favorite.

Where Trump could lose, and other things to watch for on Super Tuesday

Cruz, who campaigned with Gov. Greg Abbott and former governor Rick Perry, laced into Trump at a fired-up afternoon rally in San Antonio, accusing him of “lying to the voters” by purportedly saying one thing about immigration behind closed doors and another in public, and tore into him over his real estate company’s hiring of foreign workers.

“You don’t get to abuse our immigration laws and take advantage of American workers, and suddenly call yourself a champion of working men and women,” Cruz said. He added later: “If you don’t want to see Donald Trump as the nominee, if you don’t want to see Hillary Clinton as the next president, then stand with us, tomorrow, on Super Tuesday.”

Rubio tried to deliver a similar message, but his voice was hoarse after several days of heavy campaigning.

“I will continue to speak out until I literally have no voice left,” the senator from Florida told a rally of business people and other well-heeled Republicans in the ballroom of an upscale hotel in the Buckhead district of Atlanta.

On this day, he relied on South Carolina Gov. Nikki Haley to deliver some of the caustic lines about Trump that have become Rubio’s stump staples recently. Chants of “Marco! Marco!” filled the ballroom as Haley, a favorite of the Republican establishment, took rhetorical uppercuts at the candidate viewed by party leaders as an uncouth cancer on conservatism.

She compared Trump to an angry schoolyard bully. She ticked through his failed businesses, from Trump Vodka to Trump Mortgage. And she likened Trump to the Ku Klux Klan protesters who camped outside her office as she pushed to remove the Confederate battle flag from the South Carolina Capitol grounds.

Between Super Tuesday and March 15, the next two weeks will determine the clear frontrunners for presidential nominees.

“We saw and looked at true hate in the eyes last year in Charleston,” Haley said, referring to a massacre at a historic black church that led to the flag’s removal. “I will not stop until we fight a man that chooses not to disavow the KKK. That is not part of our party. That is not who we want as president.”

Haley’s appeal resonated with Ladonna Johnson, 36, a Web developer who has voted for Democrats in years past but plans to cast her ballot for Rubio.

“It’s really about Donald Trump,” said Johnson, who is black. “I’ve gone out there and looked for a candidate who I think can beat him, and this is it. . . . We may not have been here a few months ago for Rubio, but he’s the best chance of stopping Trump, who is racist in my eyes.”

During a CNN interview Sunday, Trump repeatedly declined to disavow the support offered by former KKK grand wizard David Duke. Condemnation rained down on Trump from Democratic and Republican leaders alike, including 2012 GOP nominee Mitt Romney, who wrote in a Twitter message that Trump’s response to questions about Duke was “disqualifying & disgusting.”

But Trump insisted Monday on NBC that he had failed to comprehend the questions from CNN anchor Jake Tapper. He said he had “a very bad earpiece” while taping the interview.

Rubio scolded Trump, telling supporters at an airplane-hangar rally in Alcoa, Tenn., “I don’t care how bad the earpiece is, ‘Ku Klux Klan’ comes through pretty clearly — and he refuses to criticize it.”

And Cruz, speaking on “The Hugh Hewitt Show” on Monday, said: “Either the Klan or Nazis, bad, bad, bad. And it seems somehow that Donald missed that briefing.”

Another controversy brewed Monday after BuzzFeed reported that Trump suggested in an off-the-record interview with the New York Times editorial board that his hard-line immigration position is more flexible than he lets on publicly.

Cruz and Rubio called on Trump to ask the newspaper to release an audio recording of the meeting, but he has not done so.

At a rowdy rally at Radford University in Virginia, Trump sold himself as the polling front-runner and as a more effective leader than either of the freshman senators. He repeatedly referred to them by demeaning nicknames — “Lying Ted Cruz” and “Little Marco Rubio” — and mocked the latter for his frequent sweating and sipping of water.

Protesters interrupted the rally at several points, drawing swift rebukes from Trump, who asked one woman if she was Mexican after a commotion. After a disruption by black attendees, who chanted slogans including “Black lives matter,” Trump shouted, “All lives matter.” The crowd cheered its approval of the candidate.

Trump also tried to signal that he was looking toward the general election, arguing that the early primary results show there is greater voter enthusiasm for him than for Democratic front-runner Hillary Clinton.

“There is enthusiasm,” Trump said of his campaign. “Big, big, big enthusiasm.”

Advisers to Rubio and Cruz hoped for a clarifying verdict Tuesday that would winnow the nominating contest to two men: Trump and one of them.

But both camps saw signs of trouble. Cruz has continued to find it difficult to unite a conservative coalition of evangelicals and self-described liberty voters. Kris Kobach, the secretary of state in Kansas and a high-profile opponent of illegal immigration, announced Monday that he was endorsing Trump, joining two fellow immigration crusaders, Sen. Jeff Sessions (Ala.) and former Arizona governor Jan Brewer, on the Trump bandwagon.

Rubio has failed so far to coalesce support within the GOP establishment. He has more endorsements on Capitol Hill than any other candidate but has struggled to convince his colleagues that he is the best alternative to Trump. Dozens of fellow GOP senators are still on the sidelines.

As Rubio and his team court more backers, their pitch is that even after Trump’s expected delegate haul Tuesday, the businessman would be only about a third of the way toward the number required to lock up the nomination. And they focus on how Rubio performed well in the early contests with voters who made up their minds in the final week or so.

Rubio’s aides have sought to roll out endorsements in specific Super Tuesday states, such as from Sen. Lamar Alexander of Tennessee, who campaigned with Rubio there Monday.

By contrast, Cruz has not received a single endorsement from the Senate; his derision of party leaders has left him with few friends in the chamber.

Further crowding Rubio’s path is Ohio Gov. John Kasich, who has turned his attention to picking up as many delegates as he can Tuesday — he sees Massachusetts and Vermont as ripe territory — and then going all-in for the March 8 Michigan primary and the March 15 winner-take-all primary in his home state.

“I’m going to win Ohio, and it’s going to be a new day when I win Ohio,” Kasich told reporters.

At a campaign event in Castleton, Vt., Jon Wallace, 54, questioned Kasich about reports that Republican leaders could use party rules to foist a nominee at a brokered convention. Wallace said he thought Kasich was an acceptable candidate but Rubio was not.

“He’s playing a conservative,” Wallace, who was wearing a pin with the Gadsden flag, the tea party symbol, said of Rubio. “He should go to Hollywood, because there’s a place in a movie for him.”

Kasich said he thought the nominee would be selected in the regular primary process, “on the up and up.” Then he bemoaned the tenor of the race.

“I have to tell you, what I’m seeing, with the name-calling, the insulting — this is no way to pick the president of the United States,” Kasich said. “It’s taking us down the rathole.”

Costa reported from Atlanta. Jose A. DelReal in Nashville; Paul Kane in Washington; Fenit Nirappil in Radford, Va.; Ed O’Keefe in Alcoa, Tenn.; and David Weigel in Castleton, Vt., contributed to this report.