WASHINGTON — (CNN) Jeb Bush is on a mission to reboot his presidential campaign and salvage boost his struggling poll numbers.

And part of that strategy is to go after Marco Rubio.

In a lengthy sit-down with CNN’s Jamie Gangel at a local restaurant here on Tuesday, the former Florida governor had no qualms pointing out repeatedly that Rubio — a first-term senator from Florida — has neglected his job in Congress since launching his White House campaign.

“People that are serving need to show up and work. Period. Over and out,” Bush told Gangel. “I just think people need to show up and work. That’s what I did.”

The former governor, however, insisted that he didn’t mean for these comments to be criticism of Rubio, his one time mentee.

“I’m not attacking to say someone should show up to work,” he said. “Do you get paid when you don’t show up? I mean, come on. Does anybody in this room get paid when they decide I’m going to go do something else?”

He went on to defend Rubio from criticisms by businessman Donald Trump, calling the senator “capable” and “talented.” But at the end of the day, Bush added, there’s no one else in the Republican field more qualified than he to be president of the United States.

Bush’s jabs at Rubio came as the ex-governor is trying to once again revamp his stalled campaign. For months, Bush has struggled in the single digits in national polls.

At the third GOP debate in Boulder, Colorado, last week, a feistier Bush took the stage. He went after Rubio for missing votes in the Senate, saying: “Marco, when you signed up for this, this was a six-year term and you should be showing up to work. What is this, like a French work week?”

But Rubio quickly hit back, essentially getting the last word in an exchange that most deemed a victory for the senator. “The only reason you’re doing it now is because we’re running for the same position,” he said.

The escalating tension between the two men, who until now have largely steered clear of going after one another on the campaign trail, signals that the campaign has turned a corner into a more competitive phase. The pressure is particularly mounting for mid-tier candidates like Bush, who have struggled to break out of the pack and catch up to the party’s front-runners.

A new NBC News/Wall Street Journal survey this week showed Bush in fifth place at 8% — far behind retired neurosurgeon Ben Carson and Trump at the top. Rubio and Ted Cruz were also ahead of Bush at 11% and 10%, respectively.

As Bush languishes in the polls and with the Iowa causes now just three months away, his team has made several moves to try to reboot his campaign.

The campaign announced drastic cuts to salaries, personnel and other costs, as part of an effort to direct more resources to the early states. Meanwhile, ex-governor’s allies have promised that voters will see a more energized and fired-up Bush on the trail — he’s confronted relentless criticism from Trump and others for lacking in energy and inspiration.

This week, Bush has taken a new campaign slogan — “Jeb Can Fix It” — on the road, to emphasize his accomplishments as Florida governor and contrast his years in the governor’s mansion against the resumes of some of his rivals who have less public service experience.

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