Kevin Lamarque/Reuters

People bow in a moment of silence for the victims of the Colorado shootings during an appearance today by President Obama in Fort Myers, Fla.

By Glen Johnson Globe Staff

BOW, N.H. - The mass shooting in Colorado cast a pall today over what has become a bitter presidential campaign, with President Obama and Mitt Romney muting anticipated attacks on each other to instead deliver somber tributes to the victims.

“We may never understand what leads anybody to terrorize their fellow human beings like this. Such violence, such evil is senseless. It’s beyond reason,” the president said during a truncated, six-minute speech in Fort Myers, Fla.

“But while we will never know fully what causes somebody to take the life of another, we do know what makes life worth living. The people we lost in Aurora loved and they were loved,” he said.

At least 12 people were killed when a gunman began shooting at the crowd in a theater in Aurora, Colo., holding a midnight screening of the latest Batman movie.

Obama, the father of young daughters, said: “I’m sure many of you are parents who had the same reaction I did when we heard the news. My daughters go to the movies. What if Malia and Sasha had been at the theater as so many kids do each day?”

The president led a moment of silence near the end of his speech.

Romney’s appearance in New Hampshire took on the air of a church service, as the pre-program music was nixed and the crowd of about 200 sat in silence.

When it was time for Romney to appear, he was preceded on stage by an Anglican priest who led a prayer.

During his four-minute remarks, Romney joined the president in seeking to humanize the moment.

“I stand before you today not as a man running for office, but as a father and a grandfather, a husband, an American,” he said in a somber tone.