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Story highlights

Some Rubio supporters questioning campaign strategy

Sen. Hatch: 'I don't think he needed to get down, deep and dirty'

(CNN) —  

Marco Rubio is putting his entire presidential campaign on the line in Florida – but some of his top supporters in Washington believe the 44-year-old senator may have already lost.

A growing number of Rubio supporters told CNN privately and publicly that Rubio made a strategic blunder by getting into a personal mud-slinging contest with the bombastic billionaire, arguing that he should not have raised questions about Trump’s character – on everything from criticizing the size of his hands to calling him a “con artist.” They argued it only seemed to backfire and make the high-minded and substantive Rubio look petty and unpresidential, fearing it could now be fatal to his presidential aspirations.

“I don’t think he needed to get down, deep and dirty,” said Utah Sen. Orrin Hatch, a Rubio supporter. “I think he knows that was a mistake. It was against his personality, and I think that hurt him a little bit.”

Added Sen. Dean Heller of Nevada, another Rubio backer: “I think the writing is on the wall: aggressively going after a candidate, or a single candidate in this race, probably wasn’t as helpful as he wanted it to be.”

“He always looked young,” said one senior GOP senator. “But that time, he acted young.”

Rubio spokesman Alex Conant declined to comment about campaign tactics. For months, Rubio avoided Trump at all costs, worried that bashing the businessman would serve little benefit to him and instead help his rivals. But, according to several advisers and people close to the campaign, Rubio calculated that it made sense to mount a vigorous assault on Trump in late February since the field began to narrow and the Florida senator didn’t have to fend off as many attacks from his rivals.

READ: Ted Cruz’s challenge: uniting Republicans against Trump

After Ted Cruz, Lindsey Graham, Jeb Bush and others failed to make much of a dent against Trump despite vigorous attacks on the real estate mogul’s core convictions, Rubio decided to level a new line of attack: Trump’s business record, contending the GOP front-runner simply got rich by hurting average Americans and scamming the system. And to Rubio’s team, attacking Trump on a personal level only seemed to energize his core supporters, prompt a flood of money online and inject himself directly into the daily news cycle.

Speaking to CNN’s Dana Bash last week at the Conservative Political Action Conference, Rubio defended his sometimes racy attacks.

’Punch them back’

“Donald Trump, he might have grown up the way he did with a lot of money and going to boarding schools,” Rubio said. “I can tell you this: Where I grew up, if someone keeps punching someone in the face, eventually someone’s going to have to stand up and punch them back.”

But on Wednesday, he acknowledged that he’s not “entirely proud” of his rhetoric.

“My kids were embarrassed by it,” he told MSNBC, adding that “if I had to do it again I wouldn’t.”

Polls have yet to show a dramatic drop in Rubio’s favorability since he sharpened his attacks against Trump. According to a Washington Post-ABC News poll conducted in early March, when Rubio’s Trump attacks were fresh and dominating the news cycle, Rubio saw little change to his personal standing, with a 39% favorable rating and 45% unfavorable – about the same from early January.

But many of his core supporters are now second-guessing his campaign tactics following his poor showing in Tuesday night’s primaries – where he has yet to be awarded a single delegate – and polls that show him getting trounced in next week’s critical Florida primary.

The fear: Attacking Trump has only served to elevate Ohio Gov. John Kasich. And after Rubio’s attacks against Cruz’s trustworthiness seemed to damage the Texas senator in the South Carolina and Nevada contests, Cruz seems now to be the beneficiary of Rubio’s laser-like focus on Trump instead.

Some top Rubio supporters say the GOP senator should hammer home his core message that attracted many to him initially – his foreign policy expertise and his lofty vows to grow the conservative movement – and avoid the back-and-forth with Trump.

“Win by what you stand for and how you’re going to get the job done,” said Sen. Thom Tillis, a No