Sen. Arlen Specter, R-Pa., said in a telephone interview from his Islamabad hotel room that he and Rep. Patrick Kennedy, D-R.I., were to dine with Musharraf and meet later in the night with Bhutto.
He said he heard about the attack on Bhutto as he was dressing for the dinner with Musharraf.
"Our foreign policy had relied on her presence as a stabilizing force," Specter said, emotionally describing her death as "a real, real, real shock."
"I knew her personally .... She was, as you know, glamorous, beautiful smart," he said. "Her loss is a setback. But you have to face what is. And now, without her, we have to regroup."
Bhutto was shot to death Thursday in a suicide attack that also killed at least 20 others during a campaign rally in Rawalpindi. She served twice as Pakistan's prime minister between 1988 and 1996 and had returned to Pakistan from an eight-year exile Oct. 18 to seek the office again.
After learning that she was dead, Specter, Kennedy and Anne Patterson, the U.S. ambassador to Pakistan, went to Bhutto's campaign headquarters, and laid flowers there under her photo.
"They were crying and they were sobbing," Specter said, describing the people there. "It's a night reminiscent of Kennedy, Robert Kennedy's assassination."
Specter described the atmosphere in Islamabad as unsettling, saying he felt apprehensive about being an American there out at night. He said he and Kennedy were cutting short their trip by a day on the advice of the State Department.