There are two working theories: He wants to be the most viable vice presidential candidate or he’s aiming for Florida’s soon-to-be-open governorship. Rubio’s campaign insists he’s focused on the presidency, but the speculation does help explain why Rubio has been so uniquely unwilling to engage the afterburners.

“Given a 16-member field you’ve got to distinguish yourself somehow, and being rather passive doesn’t seem to be a way to distinguish oneself,” said William Claggett, a political science professor at Florida State University. “And Rubio is also competing for media attention, and media likes conflict, not everybody being nice.”

Rubio’s establishment rivals facing similar woes have changed course—Jeb Bush has gone on offense against Donald Trump. Wisconsin Governor Scott Walker has crafted a scrappier stump style. Rubio meanwhile has stuck to the same theme and tone, polishing his optimistic message and his persona as a fresh conservative leader for a new era. If he falls short, it’s hard to imagine the young rising star, who has held elected office almost consistently since his late 20s, quitting politics at this juncture.

“He’s a young guy who’s got a great future ahead of him no matter what happens,” said Rick Wilson, a Florida-based Republican strategist who’s unaffiliated in the presidential contest.