Presidential candidate Sen. Marco Rubio (right) speaks while Jeb Bush looks on during the CNBC Republican presidential debate, Oct. 28, 2015, in Boulder, Colorado. Justin Sullivan/Getty Images

Where's the love, guys? Former Florida Gov. Jeb Bush called out his former political ally, Florida Sen. Marco Rubio, during a Republican debate Wednesday night in Colorado, prodding him for not working harder in the Senate. Rubio responded by pointing out Bush's tanking poll numbers.

The exchange crystallized how wide the chasm between the two Florida Republican leaders has grown in recent months, as Rubio has performed well in the polls and Bush has seen his front-runner status vanish. After Rubio was asked during the debate about his frequent absences in the U.S. Senate, Bush said Rubio had committed to six years and should ride out his term instead of running for president.

"Marco, when you signed up for this, this was a six-year term," Bush said. "I mean, literally the Senate, what is it a French work week where you have three days to show up? You can campaign, or just resign and let someone else take the job."

Rubio said Bush was lashing out. "Someone has convinced you that attacking me is going to help you," Rubio said. "My campaign is going to be about the future of America. I'm not running against Gov. Bush. I'm not running against everyone else on this stage. I'm running for president."

Rubio’s hometown paper the Sun Sentinel released an editorial this week demanding that he resign. “Your job is to represent Floridians in the Senate,” the paper wrote. “Either do your job, Sen. Rubio, or resign it.”

Bush has struggled to impress voters despite his massive campaign haul and famous last name. His campaign had billed the debate Wednesday as a relaunch after months of sinking poll numbers. His super PAC raised $100 million in the first half of this year but has since burned through the cash.

Bush was a popular two-term governor, but voters are more inclined to embrace political outsiders this campaign season. Nearly 60 percent of voters who leaned Republican told the Pew Research Center in March that experience and a proven record were the most important traits in a presidential candidate. By September, only 29 percent said they felt that way.

Part of his problem is that he can come across as entitled and bored, some pundits claim. "Bush needs to show he WANTS the Republican nomination and is willing to fight like hell for it. The problem for him -- and this has always been Jeb's problem -- is that he has always been a sort of awkward candidate, more suited to being governor (or president) than running for the office," the Washington Post noted Wednesday.

Still, Republican strategists have warned that Bush shouldn't be counted out. "Every winning nominee and every winning presidential candidate walks many lonely miles through the valley of the shadow of political death -- and resiliency is the chief virtue required for victory," Steve Schmidt, a former adviser to Republican Sen. McCain who helped his 2008 presidential campaign, told CNN. "John McCain understood that, as did Barack Obama while going through the Rev. (Jeremiah) Wright debacle, as did George W. Bush after losing to John McCain in New Hampshire in 2000, and there are many other examples."