Obama:

I am shocked and saddened by the death of Benazir Bhutto in this terrorist atrocity. She was a respected and resilient advocate for the democratic aspirations of the Pakistani people. We join with them in mourning her loss, and stand with them in their quest for democracy and against the terrorists who threaten the common security of the world.

Clinton:

"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."

McCain:

"I was deeply saddened today to learn about the death of Pakistani opposition leader Benazir Bhutto. My deepest condolences go out to the family and supporters of this remarkable woman, an individual who paid the ultimate price for her embrace of moderation and rejection of extremism.

"The death of Benazir 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."

Biden:

"I am convinced Ms. Bhutto would have won free and fair elections next week. The fact that she was by far Pakistan's most popular leader underscores the fact that there is a vast, moderate majority in Pakistan that must have a clear voice in the system. Her assassination makes it all the more urgent that Pakistan return to a democratic path.

"This fall, I twice urged President Musharraf to provide better security for Ms. Bhutto and other political leaders -- I wrote him before her return and after the first assassination attempt in October. The failure to protect Ms. Bhutto raises a lot of hard questions for the government and security services that must be answered.

"I know that Benazir's followers will be tempted to lash out in anger and violence. I urge them to remain calm -- and not play into the hands of the forces of destruction. I urge Pakistan's leaders to open a fully accountable and transparent investigation. We must find out who was behind this and bring those responsible to justice. And the United States should offer any assistance necessary, including investigative teams, to get to the bottom of this horror.

Giuliani:

"The assassination of Benazir Bhutto is a tragic event for Pakistan and for democracy in Pakistan. Her murderers must be brought to justice and Pakistan must continue the path back to democracy and the rule of law. 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:

"I am deeply troubled by the news accounts this morning of Pakistani opposition leader and former Prime Minister Benazir Bhutto's assassination in a suicide attack. This is devastating news for the people of Pakistan, and my prayers go out to them as we follow developments regarding this dire situation.

"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. On this sad day, we are reminded that while our democracy has flaws, it stands as a shining beacon of hope for nations and people around the world who seek peace and opportunity through self-government."

Richardson:

A leader has died, but democracy must live. The United States government cannot stand by and allow Pakistan's return to democracy to be derailed or delayed by violence.

We must use our diplomatic leverage and force the enemies of democracy to yield: President Bush should press Musharraf to step aside, and a broad-based coalition government, consisting of all the democratic parties, should be formed immediately. Until this happens, we should suspend military aid to the Pakistani government. Free and fair elections must also be held as soon as possible.

It is in the interests of the US that there be a democratic Pakistan that relentlessly hunts down terrorists. Musharraf has failed, and his attempts to cling to power are destabilizing his country. He must go."

Romney:

"We are still learning the details of today's tragic events in Pakistan, but this is a stark reminder that America must not only stay on high alert, but remain actively engaged across the globe. Pakistan has long been a key part in the war against extremism and radical jihadists. For those who think Iraq is the sole front in the War on Terror, one must look no further than what has happened today. America must show its commitment to stand with all moderate forces across the Islamic world and together face the defining challenge of our generation – the struggle against violent, radical jihadists.

"At this difficult time, our thoughts and prayers go to the family of Benazir Bhutto, and to all the people of Pakistan who are fighting against extremist forces that would commit such heinous acts as the whole world has witnessed today."