As U.S. officials meet with Pakistani President Asif Ali Zardari this week in Washington, there is someone missing from the discussions: Zardari's archrival, Nawaz Sharif. The two-time prime minister is back with a vengeance -- and an approval rating more than three times that of the president. Now he is hoping for another chance at power. He has the political winds at his back. But can he be trusted to govern?

Head of his own wing of the Pakistan Muslim League party, Sharif is marketing himself at home and in Washington as a bulwark of democracy against the rising tide of Talibanization. In an April interview with USA Today, for example, he criticized Taliban militants for advocating a harsh version of sharia and vowed to roll back their territorial gains.

Sharif's timing has never been better. Taliban insurgents were within 60 miles of the capital last week; a government peace deal with pro-Taliban clerics in the Swat Valley has fallen apart; and despite recent upticks in effort, the Pakistani military seems unable (or unwilling) to truly engage in the fight.

Some improvements in the situation -- of the kind Sharif promises -- would be music to American ears. And unlike the Bush team, which preferred to work through former Pakistani President Pervez Musharraf, the Obama administration is willing to hedge its bets. U.S. officials are actively courting opposition leaders, and especially Sharif.

So who is Nawaz Sharif? The politician has come a long way since his controversial start as a firebrand protégé of Islamist general and former Pakistani President Mohammad Zia ul-Haq. Like most ambitious politicians, he developed strong ties with the Pakistani military and intelligence officers and gave full support to the Afghan jihad against the Soviets in the 1980s.

Since then, Nawaz has reinvented himself as a constitutional liberal, an audacious if not entirely persuasive feat of political shrewdness. His two stints as prime minister in the early and late 1990s were marked by weak economic growth, widespread corruption, and ineffective governance. Still, he is remembered less for his failures than for authorizing the 1998 nuclear tests that made Pakistan the first, and so far only, Muslim country with a nuclear bomb.

More recently, Sharif owes his popularity to savvy moves such as his unbridled support for Pakistan's recently reinstated chief justice, Iftikhar Muhammad Chaudhry, who was twice removed unconstitutionally by Musharraf. Bold street protests led by Sharif forced the judge's reinstatement this year. He is a staunch supporter of constitutional reform including granting the rustic Baluchistan province more economic autonomy to keep a cap on a dormant insurgency there. Even Sharif's anti-American rhetoric has mellowed from fighting imperialism to asking for respect for Pakistani sovereignty.

Could Sharif use his popularity, and his Islamist credentials, to tame the Taliban? He does have a long and intimate relationship with Pakistan's premier intelligence agency, Inter-Services Intelligence, which he has often put to use in swallowing up Islamist parties into his larger political structure and base. Moreover, Sharif has encouraging experience with urban counterinsurgency. In the early 1990s, he used effective (albeit unaccountable) policing to quell an uprising in Karachi -- an 18 million-strong tinderbox of ethnic, criminal, and religiopolitical forces. Today, with Pakistan's cities threatened by even deadlier forces, such as al Qaeda and the Taliban, it might help that Sharif is no novice.

Of course, there are caveats. Sharif was successful in Karachi during his term but later capitulated to Islamists in the Swat Valley. He acquiesced to a pact with the Islamist parties in the late 1980s for political expediency. Then in the late 1990s, he showed little resistance to Islamists as they called for laws to reduce religious freedom and gender equality throughout Pakistan. Sharif introduced a 1998 bill intended to impose strict sharia nationwide and make him the supreme leader, Iran style -- able to challenge any legislation that he deemed inconsistent with the Koran and the country's Islamic Constitution.

Sharif's supporters in the United States -- and he has some -- contest that this Islamist-leaning prime minister is now "dead." Today he is a patriotic demagogue, they say, willing and ready to defend his country from either Taliban or U.S. dictates. One might even argue that Sharif's previous experience taught him the perils of cutting deals with Islamists in Pakistan's northern frontier -- as the government of Zardari has just done.

Whether the White House believes that story or not, President Barack Obama is likely to keep his options open. The stakes in Pakistan are too great for the U.S. president to rely solely on one leader. If in the next 12 to 18 months the Taliban's gains are not reversed, don't be surprised if Washington pushes for political change in Islamabad, starting with Nawaz Sharif as prime minister. (Many expect the newly reinstated chief justice to help clear the charges of corruption currently preventing him from running.) From there, Zardari could be coerced to step down with the help of the military, notably Army chief Gen. Ashfaq Parvez Kayani, and new parliamentary elections could be organized.

Presently, Zardari and Sharif will undoubtedly try to make political gains from the country's reigning instability. They would do well to realize that this time around, there will be no blank checks -- from the United States or the Taliban.