“There’s a lot of angst about him running” for President, says one veteran Republican consultant, who believes Rubio’s bid for the Oval Office is a long shot. “He would’ve held onto the [Senate] seat. He’s a terrific fundraiser, and it probably wouldn’t have been as competitive.”

Republicans have a deep bench in Florida. “Florida Republicans have consistently demonstrated a proven capacity to win statewide races and we look forward to electing another strong Republican like Senator Rubio,” says Kevin McLaughlin, deputy executive director of the NRSC. But the GOP Senate campaign arm may struggle to recruit a candidate of comparable strength. Already two top potential candidates, state chief financial officer Jeff Atwater and former state House speaker Will Weatherford, have passed on the race.

Meanwhile, U.S. Rep. Patrick Murphy has announced a run for the Democratic nomination. In the absence of Rubio, the race could be one of the nation’s toughest. Last month the Democratic firm Public Policy Polling surveyed hypothetical match-ups between eight leading prospective contenders from both parties; on average, the Democrat led by less than one point. Rubio, in contrast, was running well ahead of top Democratic rivals.