Jacksonville, Florida (CNN)As rivals, Jeb Bush repeatedly called Marco Rubio a "backbench" senator of little accomplishment, accused him of "cutting and running" on the Gang of Eight immigration bill, and suggested he has nothing in his background that would indicate he could make a "tough decision."
Ahead of Florida, Jeb Bush still weighing Marco Rubio endorsement
Now the former Florida governor, who dropped out of the 2016 race last month, has to decide whether he's going to endorse his former opponent ahead of Florida's all-important primary on March 15.
A former Bush campaign official who asked not to be identified to speak more freely believes it's a "possibility" Bush will endorse Rubio, especially if Bush thinks it can "make a big difference and slow Trump down."
The former campaign official said an endorsement would not be awkward, even though things between Bush and Rubio got ugly toward the end of Bush's campaign.
"I think the governor was pretty straight about it, that he always said, 'This is my view on (Rubio's) experience and accomplishments, but he's a friend.' I think the governor's a big enough of an adult to forget that stuff. I don't think that's going to keep (an endorsement) from happening," the former campaign official said.
At the same time, this source also thinks that an endorsement from Bush isn't something that's going to make or break Rubio's bid in Florida.
"It's a lot more hype than real tangible votes," the source said, adding that Rubio is capable of winning Florida without Bush's help.
Ana Navarro, a former Bush supporter and friend of Rubio's, said Bush will "follow his gut" but she's not sure a Bush endorsement would mean much. In an email, she noted that Rubio was endorsed by Gov. Nikki Haley in South Carolina, Gov. Sam Brownback in Kansas, Gov. Bobby Jindal in Louisiana -- and lost all three states.
"Just doesn't feel like endorsements matter as much this cycle," Navarro, a CNN contributor, said.
Two Bush advisers who asked not to be named also said Bush has not made a decision yet.
"Jeb is watching and waiting," one adviser told CNN. "Endorsement not committed or imminent."
Florida, with its 99 delegates, is widely considered Rubio's last stand. He's confident he can win his home state, but he faces a tough challenge against the current front-runner, Donald Trump. A Quinnipiac Poll released late last month showed Trump with a double-digit lead over Rubio in Florida, 44%-28%.
Texas Sen. Ted Cruz is also making a play for Florida, mostly to thwart any momentum for Rubio in an effort to narrow the race to a two-man contest between Cruz and Trump.
An endorsement from Bush, who left his second term as governor in 2007 with a 64% approval rating, would generate significant buzz, and some believe it could help tip the scales for Rubio.
Bush had the overwhelming majority of support from elected Florida officials over Rubio when he was still a candidate, including eight of the current and former House speakers -- a fact that Bush made sure to tout on the campaign trail.
Since Bush dropped out, many in the Florida political class have switched to Rubio, including U.S. Reps. Ileana Ros-Lehtinen and Mario Diaz-Balart of South Florida.
Bush's spokeswoman said the former governor has no news to announce on any potential endorsement. But as the primary nears and all eyes turn to Florida, the pressure is mounting.
Nelson Diaz, the chairman of the Miami-Dade County Republican Party, said it "would certainly be helpful" because Bush is "very well respected in Florida."
He questioned why Bush hasn't offered his support yet, given that early voting is already well underway.
"I've heard from a lot of party -- longtime party -- folks, asking me why Bush hasn't done it yet, that it would be very noble of him to do it," said Diaz, who is personally supporting Rubio but whose group is staying neutral. "If Bush wanted to ensure Trump doesn't win, that would be the best way to do it."
Though Bush wasn't successful in his own bid, he went down fighting against Trump, charging the billionaire businessman of "hijacking the conservative cause" and saying he disparages women, Hispanics and the disabled.
But in the final months of his campaign, he also ramped up his attacks against Rubio, his former protégée when Bush was governor and Rubio was rising in the ranks of the Florida House to eventually become speaker.
While still trying to describe him as a friend, Bush nonetheless ripped into Rubio for missing votes in the U.S. Senate and even called on the first-term senator to resign on a national debate stage last fall.
In turn, Rubio blasted Bush for lacking foreign policy experience, and made veiled references to the candidate's age.
In 2012, Bush refrained from endorsing a candidate before the heated Florida primary that was mostly fought between Mitt Romney and Newt Gingrich, so it wouldn't be unprecedented if Bush decided to hold back.
CNN's Dana Bash asked Rubio on Saturday whether he's approached Bush for his support. The senator declined to discuss his private discussions with Bush but said he has admiration for him and welcomes as many endorsements as he can get.
"I will always have tremendous affection and respect for him despite the fact that -- because of a weird quirk of fate -- we ended up running for the same office at the same time," Rubio said. "I did not run for president to stop Jeb Bush. I ran for president because I believe that America's greatest days lie ahead if we do what needs to be done right now in 2016."