Jeb Bush and Marco Rubio: The Frenemies of 2016

— -- As is always the case in politics, there are friends and foes, allies turned archrivals.

But for GOP candidates Jeb Bush and Marco Rubio, the relationship is far more nebulous. The longtime mentor and protégée are now seeing themselves forced into a rivalry by a primary that, whether they like it or not, has pitted the two Floridians against each other.

And while they still attempt to remain civil, the long-brewing battle between the two camps is slowly bubbling up.

Bush's son, Jeb Jr., unleashed on the senator while speaking to a group of College Republicans in New York last week.

“As a Floridian, I’m a little disappointed, because he’s missing, like, 35 percent of his votes,” Jeb Bush Jr. said of the U.S. senator from Florida, according to Politico. “And it’s just, kind of, like, dude, you know, either drop out or do something. But we’re paying you to do something; it ain’t run for president.”

Rubio has missed 29 percent of Senate votes in the past year.

Jeb Bush Jr.'s words went much further than his father’s, who usually speaks in generalities about Rubio's missed Senate votes, choosing instead to allude to his performance without invoking Rubio by name unless asked specifically.

When asked by reporters in New Hampshire about whether Rubio is shirking his responsibilities, Bush, 62, toed his oft-walked line of civility.

"I just think you have a responsibility to serve. And some of these votes actually matter, defense appropriations bills matter, committee hearings dealing with real challenges that our country faces. Marco's got great ideas on these things, but he got elected to serve,” Bush said.

Rubio has been somewhat reluctant to fight back.

“When candidates are running, I think they’re going to say things that they think will make them stronger in the race. They’re going to attack people,” he told reporters who asked about Bush’s comments a few days later.

“I have great admiration and respect for [Bush] as a person. I’m not running against Jeb Bush. I’m running for president,” he added, reiterating the usual response he has given to questions about Bush since he first joined the race.

Rubio has, indeed, spent a lot of time praising his former mentor, something mutual rival Donald Trump has picked up on, attacking both Bush and Rubio for their “hypocrisy.” In 2012, Bush told Charlie Rose that Rubio had "more experience that Barack Obama had when he ran," an apparent contrast to the inexperienced “insider” portrait he now paints of him.

"He's certainly got the intellectual acumen and the fortitude to be a good president,” Bush then said.

Meanwhile, Rubio is doing his own dance in trying to distinguish himself from his former mentor.

“Governor Bush was a great governor of Florida, I never dispute that,” Rubio has said.

But asked in Iowa whether he was the better candidate, Rubio wasted no time beating around the Bush.

“Obviously. I wouldn’t run for president if I thought somebody else was a better candidate,” he said.

“It’s not a personal slight against anyone else in the field. I have tremendous admiration and respect and affection for Jeb,” Rubio insisted.

Out on the stump, however, Rubio, 44, makes the case that America needs to elect "a new generation of leadership" and "turn the page" on the leaders of "yesterday." In doing so, Rubio subtly takes aim at both Bush, 62, and Hillary Clinton, 67.

“If we keep electing leaders from the past, we are going to continue to get the same results,” he often says.

The pair's relationship began back in 1996, when Rubio worked on Bob Dole's campaign. Bush also donated to Rubio’s campaign when he ran for local office. Fast forward nearly 10 years: It’s 2005, Rubio has been voted next in line in the State House. Bush, then-governor, presented him with a sword, symbolically knighting him as Florida's rising star. At the time, Bush said “I can’t think back to a time when I was prouder to be Republican.”

But now, Rubio presents Bush as perhaps his most credible threat. Bush advisers maintain that front-runners Donald Trump and Ben Carson don't worry them, but confide that it is Rubio who concerns them most.

“There are a few young candidates running on the idea of ‘Tomorrowland,'” said Al Cardenas, a longtime GOP operative and Bush supporter who knows both men. “Rubio has always worried me the most.”

The Rubio campaign won’t comment on whom they see as their biggest threat, but recent developments indicate the fear is mutual. With last quarter's fundraising numbers coming out, the battle has turned financial.

When news first broke, it appeared as though Rubio had bested Bush; Rubio had $11 million cash on hand, Bush $10.2 million.

“Marco Rubio for President started October with more money in the bank than Jeb Bush for President and most other campaigns,” the Rubio campaign boasted in a news release.

A closer analysis of the numbers, however, revealed a different story. Rubio’s $10.9 million cash on hand includes $1.2 million in general election funds, which can’t be used unless Rubio wins the nomination.

Without that extra $1.2 million, it turns out Rubio has less cash on hand than Bush.

Yet again, Bush kept mum, while his surrogates did the dirty work.

The Super PAC, Right to Rise, that is backing Bush, has also had its sights set on Rubio, sending trackers to two of his events (one in Cedar Falls, Iowa, the other in Las Vegas).

When asked to confirm that the tracker was theirs, spokesman Paul Lindsay told ABC: "And we thought Donald Trump was thin-skinned. It's a wonder why Marco Rubio has such a problem with transparency.”

In Iowa, Rubio shrugged off the trackers.

“Doesn’t matter. I’m campaigning, and when I’m campaigning, either somebody else tracks it or you guys get it on video; people will know what we’re saying,” he said.

Still, both times, the Rubio campaign opted to kick the trackers out.

For now, Bush still uses his own record as his best defense, trying to stave off what could be an inevitability, having to go head-to-head with the candidate whose career he helped to shape.

"Look, I’m a friend of Marco’s. I’m a huge fan of his," Bush told reporters last week in New Hampshire. "I got to work with him, he got to work with me. That’s a better way of saying it. When I was governor, he was an incredible talent, but we’re in times right now that I think requires leadership and that’s my case, and I’m going to stick with it. "