Story highlights A South Florida newspaper isn't endorsing in the Republican presidential primary

The lack of an endorsement stings Rubio, who needs to win Florida's March 15 primary

(CNN) A major South Florida newspaper's editorial board says it can't endorse any of the 2016 Republican candidates -- a rebuke that especially stings Florida Sen. Marco Rubio.

The Broward County-based Sun-Sentinel's decision comes as Florida's 99-delegate, winner-take-all March 15 primary approaches.

A win there is particularly key to Rubio, who has fallen behind Republican front-runner Donald Trump and Texas Sen. Ted Cruz in the race for delegates. A Monmouth University poll released Monday shows Rubio is strongest in the southern part of the state.

But the Sun-Sentinel, which had initially backed Jeb Bush in the GOP primary, lambasted Rubio, writing that he "has almost no experience and has done little but run for office," and criticizing his missed Senate votes.

"Because Rubio has failed to do his job as a senator, broken the promises he made to Floridians and backed away from his lone signature piece of legislation on immigration, we cannot endorse him for president," the newspaper wrote.

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