In Washington, the ultimate Pakistani nightmare is that the country's nuclear arsenal could fall into the hands of Taliban militants or rogue soldiers.
In Islamabad, though, talk of nuclear weapons taps into a very different fear: Washington.
The United States, they'll tell you in this capital city of well-ordered neighborhoods and retired generals, wants to seize Pakistan's arsenal. And as Pakistan spirals into ever-worse bloodshed, they worry Washington might find an excuse.
On Tuesday, a suicide bomber attacked a crowded northwestern market, killing 24 people. In the most audacious assault, militants stormed the Pakistani army headquarters last month, raising fears around the world of a security apparatus that has trouble protecting its own generals _ let alone a nuclear arsenal estimated at 70-90 warheads.
There is "a unilateral U.S. plan to have a force in Pakistan to attempt to take out the (nuclear) triggers and thereby decapitate the nukes," Shireen Mazari, editor of the prominent English-language newspaper The Nation, wrote in a front-page editorial. "Is that why we are seeing so many covert U.S. personnel coming into Pakistan?" she continued, a reference to the widespread belief that American military contractors are slipping into the country.
Such talk reflects the delicate and often contradictory nature of Pakistan-U.S. relations as well as the peculiar role that nuclear weapons play in Pakistan's self-image.
Certainly not every Pakistani is worrying about American nuclear commandos, but it's far from just the extremist fringe. Although Washington has given billions of dollars in aid to Pakistan over the years, the U.S. is also seen here as an untrustworthy ally willing to betray its friends without warning.
Polls have repeatedly shown that many Pakistanis are highly distrustful of the United States, and that many even view the U.S. as an enemy. In the streets, it's easy to find people who blame the recent surge in violence not on the Taliban, but on the CIA or the tarnished U.S. security contracting company once called Blackwater.
Washington's warming ties with archrival India do little to ease suspicions among Pakistanis, many of whom see an Indian hand behind most of the country's troubles.
In many ways, though, it's easy to see why people are suspicious. Ties between Washington and Islamabad are seldom clear. CIA drone aircraft, for instance, regularly fire on militants in isolated Pakistani villages. While top Pakistani leaders would privately have to approve such attacks, those officials _ sensitive to public fears _ publicly rail against the drone strikes and demand the U.S. end them immediately.
As for nuclear weapons, in Pakistan they are far more than just a secretive branch of the defense ministry.
"Look here, this is our most important totem pole, our nuclear capability," said opposition lawmaker Ayaz Amir.
The current round of hand-wringing was set off this week by an article in The New Yorker questioning Pakistan's nuclear security. It said Washington had detailed knowledge of Pakistan's arsenal, had worked with Islamabad to harden nuclear installations and had trained a secret team that could secure the weapons in case of a crisis.
While questions about nuclear security have been raised for years, and the existence of a U.S. team has long been rumored, Pakistan's response was immediate, angry and loud.
_ "Preposterous," said the Foreign Office.
_ "Absurd," said the chairman of the Joint Chiefs of Staff.
_ "Fantasies," said The Nation.
Such reactions _ a mix of defensive outrage and fury that their own government might be giving nuclear secrets to Washington _ don't surprise people who watch this country.
"Nuclear status is an extremely important issue for Pakistan," Hassan Abbas, a former top government official now at Harvard University's Belfer Center for Science and International Affairs, said in an e-mail. "Especially at a time when it is faced with multiple life-threatening challenges."
Pakistan's nuclear weapons program is many things here. It is a sign of Pakistan's technological prowess and it's a point of pride that Pakistan has the Muslim world's only nuclear missiles. It is also, they say, a strategic insurance policy, a way to ensure that Pakistan cannot be obliterated in an atomic firestorm launched by India. At the very least, Pakistan will be able to fire back.
But Pakistan also has plenty of challenges. Taliban fighters have staged a wave of increasingly bloody attacks against civilian and military targets over the past few months, raising the violence after a government offensive began in October in the semiautonomous region of South Waziristan. The rugged mountainous tribal area, just across the border from Afghanistan, is the main Pakistani stronghold for the Taliban and al-Qaida.
The militant attacks have reached far from those strongholds, leaving more than 300 people dead since the beginning of October. Suicide bombers have hit public markets and a U.N. office; gunmen have killed one general in the streets of Islamabad and injured another; commando-style raids paralyzed the eastern city of Lahore.
Most alarming, though, was the October storming of the Pakistani army headquarters, in the nearby city of Rawalpindi. The attack lasted 22 hours, left 23 people dead and brought Taliban fighters into the heart of the country's powerful security establishment.
In public, Washington insists it is confident of Pakistan's nuclear security.
"The United States has no intention to seize Pakistani nuclear weapons or material," U.S. Ambassador to Pakistan Anne Patterson declared in a statement. The New Yorker article, though, insists Washington is _ in private _ very worried.
But inside Pakistan, it is heresy to raise such concerns, and many people can reel off the nuclear safeguards: strict oversight of personnel, physical separation of weapon components, complex locking systems.
"It is under secure lock and key and no one can come near it," said Amir, the opposition lawmaker.