Obama sought to temper the campaign spirit of those at his event to fit the mood of the day. He thanked his supporters and said he had looked forward to talking about the differences between Romney and him, saying instead: "This, I think, is a day for prayer and reflection."
Nevertheless, as the end of his remarks about a nation that supports its own and appreciates its blessings, Obama's supporters added a political touch by chanting "Four more years!"
It remained to be seen whether the episode would inject the volatile issue of gun rights — an issue largely missing throughout the months of campaigning so far — into the election debate.
New York Mayor Michael Bloomberg, in a radio interview, admonished both the president and his challenger to forcefully address gun violence.
"You know, soothing words are nice, but maybe it's time that the two people who want to be president of the United States stand up and tell us what they are going to do about it, because this is obviously a problem across the country," he said.
Obama said he viewed the moment through the eyes of a parent. He and his wife have daughters who turned 14 and 11 this year.
"What if Malia and Sasha had been in the theater?" he asked. "Michelle and I will be fortunate enough to hug our girls a little tighter tonight, and I'm sure you will do the same with your children. But for those parents who may not be so lucky, we have to embrace them and let them know we will be there for them as a nation."
The shooting brought a halt to political events around the country.
Many were canceled or postponed Friday, from Senate Republican Leader Mitch McConnell's news conference on Capitol Hill to a Democratic event in Reno, Nev., on funding for an alert system for missing children. Biden canceled a fundraiser in Texas, and first lady Michelle Obama did the same for planned campaign events in Virginia. Romney's wife, Ann, called off her scheduled event in Michigan.
The tragedy inspired unifying statements, rather than partisan pronouncements, from the nation's leaders.
"I join President Obama, and every American, in sending my thoughts and prayers to the victims of this awful tragedy," said House Speaker John Boehner, R-Ohio. "We will all stand with them, as one nation, in the days ahead."
"The thoughts and prayers of all members of Congress are with Coloradans this morning," said House Democratic Leader Nancy Pelosi, D-Calif.
In Fort Myers, there was none of the customary music to usher the president out. People seemed sad as they left.
Said Diane Buckley of Fort Myers: "I liked that someone in a position of leadership can be as emotional as that and take a moment to value the people we love and to reach out to others."
Associated Press writers Jim Kuhnhenn, Ben Feller, Mark Smith and Laurie Kellman in Washington, Tamara Lush in Fort Myers, Fla., and Steve Peoples in Bow, N.H., contributed to this report.
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