“It’s kind of hard to imagine that my good friend Marco would be critical of his good friend Jeb”

“It’s kind of hard to imagine that my good friend Marco would be critical of his good friend Jeb,” Mr. Bush told reporters with a smile.

The remarks by Mr. Rubio, 44, which kicked off the event hosted by Gov. Rick Scott of Florida, a fellow Republican, was a less-than-subtle attack at what Mr. Rubio considers an older, out-of-touch generation of politicians, but he didn’t mention Mr. Bush by name.

The two men were once quite close, with Mr. Bush serving as something of a mentor to Mr. Rubio. But now they are likely headed to a contentious nominating fight, with each scrambling to line up loyalists, particularly in Florida, a crucial primary state with a rich trove of delegates.