Giuliani:

Giuliani said the assassination underscored a need for the U.S. to increase its efforts to combat terrorism. "Her murderers must be brought to justice, and Pakistan must continue the path back to democracy and the rule of law," Giuliani said in a statement. "Her death is a reminder that terrorism anywhere — whether in New York, London, Tel-Aviv or Rawalpindi — is an enemy of freedom. We must redouble our efforts to win the terrorists' war on us."

Huckabee:

Huckabee said the assassination was "devastating news for the people of Pakistan, and my prayers go out to them." "The terrible violence surrounding Pakistan's upcoming election stands in stark contrast to the peaceful transition of power that we embrace in our country through our Constitution," Huckabee said in a statement.

McCain:

McCain, in a statement, said the death of Bhutto "underscores yet again the grave dangers we face in the world today and particularly in countries like Pakistan, where the forces of moderation are arrayed in a fierce battle against those who embrace violent Islamic extremism.

"Given Pakistan's strategic location, the international terrorist groups that operate from its soil, and its nuclear arsenal, the future of that country has deep implications for the security of the United States and its allies. America must stand on the right side of this ongoing struggle," he said, noting that he has made numerous visits to Pakistan.

Romney:

"This type of loss of life points out again the need for our nation and other civilized nations of the West and Muslim world to come together to support moderate Islamic leaders and moderate Islamic people to help them in their effort to reject the violence and the extreme," Romney told reporters after his first campaign event at Norton's Classic Cafe, in Hudson, N.H. "The world is very much at risk by virtue of these radical, violent extremists and we must come together, in great haste and great earnestness, to help overcome the threat of the spread of radical, violent jihad."

Romney was also asked whether he stands by his criticism of Musharraf for imposing martial law:

"I believe it was a mistake. I believe as well that martial law was principally imposed by him to protect himself from political challenge, a challenge from the Supreme Court and others, and believe that it was not a productive course for his nation," Romney said.

Update: Hillary's full statement:

"I am profoundly saddened and outraged by the assassination of Benazir Bhutto, a leader of tremendous political and personal courage. I came to know Mrs. Bhutto over many years, during her tenures as Prime Minister and during her years in exile. Mrs. Bhutto's concern for her country, and her family, propelled her to risk her life on behalf of the Pakistani people. She returned to Pakistan to fight for democracy despite threats and previous attempts on her life and now she has made the ultimate sacrifice. Her death is a tragedy for her country and a terrible reminder of the work that remains to bring peace, stability, and hope to regions of the globe too often paralyzed by fear, hatred, and violence.

"Let us pray that her legacy will be a brighter, more hopeful future for the people she loved and the country she served. My family and I extend our condolences and deepest sympathies to the victims and their families and to the people of Pakistan."

Update: John Edwards (received by e-mail):

"Benazir Bhutto was a brave and historic leader for Pakistan. Her assassination is a sad and solemn event, and our hearts go out to her family and to the Pakistani people. But we will not let this contemptible, cowardly act delay the march of progress in Pakistan for a single second. "I have seen firsthand in Pakistan, and in meetings with Prime Minister Bhutto and President Musharraf, the instability of the country and the complexity of the challenges they face. At this critical moment, America must convey both strength and principle. We should do everything in our power to help bring the perpetrators of this heinous act to justice and to ensure that Bhutto's movement toward democracy continues."