MANALAPAN, Fla. (AP) — President Barack Obama is warning Florida retirees that Republican challenger Mitt Romney would undercut the new health care law and alter Medicare, a play for voters in one of the nation's top swing states.

Obama on Friday was cutting short a two-day trip to Florida after a stop in Fort Myers. A second event, scheduled for suburban Orlando, was canceled because of the developing story in Colorado, where a gunman opened fire at a suburban Denver movie theater, killing 12 people. Obama was expected to comment on the shooting at his campaign rally in Fort Myers, then return to the White House earlier than originally planned.

The day's tragic events also forced schedule changes for Obama's Republican rival, Mitt Romney, who canceled several radio interviews he was scheduled to tape Friday. But he was  going ahead with an appearance in New Hampshire.