By M Ilyas Khan
BBC News, Karachi
The attack on Benazir Bhutto proves once again that the greatest enemy Pakistan faces comes from within.
The PPP is enraged over one of Pakistan's worst suicide attacks
Thursday night's bombers in Karachi targeted a rally that was widely seen as a demonstration by hundreds of thousands of Pakistanis who wanted to show their faith in liberal, secular democracy.
Ms Bhutto, twice prime minister, was able to demonstrate she remains the country's most popular leader, and that she offers an alternative to the rising anti-Americanism of Pakistan's
In the view of some analysts, this is important to prevent the country from becoming a pariah state.
What the blasts prove is that no amount of security can succeed in a country where state institutions have remained above public accountability and often work at cross-purposes.
Pro-Taleban militants in the north-west are seen as the most obvious suspects behind the blasts in which scores died and many more were wounded.
In recent weeks, at least two top militant leaders had warned that Ms Bhutto, a "slave of the US", may face suicide attacks.
The Karachi-based Muttahida Quami Movement (MQM) party is also seen as a possible suspect.
In the past, it has had strained, often violent relations with Ms Bhutto's Pakistan Peoples' Party (PPP).
But it is not known to carry out suicide bombings, if that is what Thursday's attacks were.
Observers point out that the MQM has been cautious, even accommodating, towards a possible power-sharing relationship between the PPP and Gen Musharraf.
As a liberal and secular party itself, the MQM is on the same side of the fence as the PPP in the emerging political scenario.
Letter to Musharraf
Ms Bhutto herself has pointed to what she says is a deeper malaise than a straightforward militant threat.
Ms Bhutto has vowed to fight extremism
Asked recently if the threats to her life emanated from al-Qaeda and the Taleban, she said the Taleban "may be used" in such an attack.
In a more recent news briefing in Dubai, she indicated that her life may be threatened by some "elements" within the government, including some "retired army officers".
She said that she had written a letter to Gen Musharraf, spelling out her security needs as well as a list of names of those who would be responsible if anything happened to her.
By implication, this meant that Ms Bhutto suspected some sections of the Pakistani intelligence apparatus and some politicians of having a motive and the ability to use militants to kill her.
The PPP, being avowedly secular and led by a woman, was the obvious target of both the establishment and the Islamic militants.
Ms Bhutto's recent claims are certain to start a new round of arguments in the country.
One reason why she went ahead with a street rally was to establish her credentials as a leader who could carry the masses, even though many had criticised her controversial move to reach an understanding with Gen Musharraf.
Some are critical of her decision to hold a rally with such obvious security risks.
Important questions now face Pakistan, the first of which is the outcome of parliamentary elections scheduled for January.
06 Oct: Presidential polls held
17 Oct: Supreme Court resumed hearing challenges to Musharraf candidacy
18 Oct: Benazir Bhutto's homecoming
15 Nov: Parliamentary term ends and general election must be held by mid-January
Gen Musharraf will be eager for his ally, the PML-Q, to perform well.
The party provides him with an important vote bank in Punjab province, where the PML-N party of exiled Prime Minister Nawaz Sharif is also powerful.
The president will no doubt be wary of an onslaught by a resurgent PPP, which could perform well in Punjab and in its traditional stronghold in the province of Sindh.
The PPP's relationship with Gen Musharraf is complicated, but most analysts agree that the more seats it wins in parliament, the less responsive it will be to Gen Musharraf's orders. He may find it hard to throw them out of power.
The president's position could be further weakened if he quits the army, although it's thought that he will still keep his power to dismiss governments.
At the same time, the president will no doubt be bearing in mind that a weakened PPP is unlikely to prove effective against the spread of militancy, an objective for which the two sides came together in the first place.
It seem that Gen Musharraf now has two options.
He can either clip the PPP's wings and continue his monopoly of power, or he can sacrifice some of his authority to back Ms Bhutto and her popular appeal to defeat militants and isolate their supporters.