At a rally in Kennesaw, Ga. on Feb. 27, Republican presidential candidate Marco Rubio responded to rival Donald Trump's comments about him wearing makeup during the CNN/Telemundo debate. (Reuters)

Real estate mogul Donald Trump’s chief rivals for the Republican nomination made an urgent push Saturday to characterize him as a dishonest candidate who has fooled Republican voters with promises he cannot keep.

But with polls showing Trump increasingly poised to secure major victories in the March 1 Super Tuesday primaries, it remains to be seen whether their escalating rhetoric will make a difference before voters cast their ballots in two days.

“I believe there are Americans today that are being fooled by this guy. I really do,” Sen. Marco Rubio (Fla.) told voters in Birmingham, Ala., on Saturday. “What’s at stake is the Republican movement. I am not going to stand by and watch the conservative movement be taken over by someone who is not a conservative.”

The senator has hurled unusually personal attacks at Trump in recent days regarding the billionaire’s motivations, his demeanor and even his age. Rubio has been particularly intent on undermining Trump’s business record, characterizing him as an entitled heir whose success was based on his family’s connections and money.

“I very rarely try to attack other Republicans because I don’t like it; I think the Democrats love when we do that. I think they cheer when we do that,” Rubio said, defending his recent shift in strategy. “But we’ve come to a point now where we have no choice but to talk about these differences.”

Sen. Ted Cruz (Tex.), speaking in Atlanta on Saturday at the Liberty Plaza, told supporters that Tuesday is the “most important day in this entire cycle.” At stake, he said, is whether the Republican Party will be able to fend off Democratic front-runner Hillary Clinton in the fall. “If we nominate Donald,” he said, “we end up electing Hillary as president.”

Cruz, at a rally in Little Rock put on by a super PAC supporting him, cited a lawsuit that accused Trump of knowingly hiring undocumented immigrants to work on Trump Tower. Trump lost the lawsuit, appealed and it was ultimately settled.

“He put his name on it,” Cruz said of Trump Tower. “Maybe it should say underneath: ‘Built by illegal immigrants.’­ ”

But Trump’s conservative credentials have been bolstered by a series of high-profile endorsements. New Jersey Gov. Chris Christie joined Trump in Bentonville, Ark., on Saturday, one day after throwing his support behind the billionaire. The Trump campaign announced Saturday that former Arizona governor Jan Brewer, a Republican firebrand who rose to national prominence because of her hard-line stance on immigration reform, had also endorsed him.

Those endorsements could be the first of many by such Republican leaders.

Trump fought back against those attacks in Bentonville, where he and Christie took turns criticizing Rubio. Trump called him “little Rubio,” a “total lightweight,” and mocked his physical appearance.

“I watched this lightweight Rubio, total lightweight, little mouth on him, ‘bing, bing, bing,’ ” Trump said, parodying Rubio’s attacks. “The last thing I am is a con man.”

Count the swipes Republican presidential candidates Marco Rubio and Donald Trump took at each other the day after they butted heads at the Houston CNN/Telemundo debate. (Sarah Parnass/The Washington Post)

As Trump spoke, a man in the crowd shouted: “Rubio’s a liar!”

The pro-Rubio Conservative ­Solutions PAC has poured millions of dollars into attacking Trump in the days before Tuesday’s voting.

“He thinks we’re fools,” says one ad from the group. “Trump uses sleazy bankruptcy laws to avoid paying workers. He bans disabled veterans from his high-rise. He even tried to use eminent domain to kick a widow from her home.”

Trump faced sustained air attacks backed by millions of dollars in South Carolina but emerged unscathed with a double-digit victory. But as the target on his back grows, a national advertising effort across multiple states could wear away at his populist support.

Trump’s critics acknowledge that the 11th-hour attacks from Rubio and others may come too late to make a difference Tuesday.

But that is not to say they are in vain. Trump’s detractors hope that sustained attacks against his business record and character will stymie his momentum ahead of the March 15 primary contests, many of which award delegates on a winner-take-all basis.

Katie Packer, a former deputy campaign manager for Mitt Romney who leads an anti-Trump super PAC, said that she thinks Rubio has a clear path forward if candidates such as Ohio Gov. John Kasich drop out of the race.

“All of the suggestions that Trump can’t be stopped comes from this suggestion that he’s impenetrable,” Packer said. “We have no idea if he’s impenetrable because nobody has ever tried to take him down.”

“None of us are going to be surprised when Trump does well on Super Tuesday,” she added. “This stuff takes a little time to sink in.”

Katie Zezima in Little Rock, Dave Weigel in Birmingham, Ala., and Jenna Johnson in Bentonville, Ark., contributed to this report.