When President Barack Obama delivered a rare public call last week for President Hamid Karzai to crack down on corruption in Afghanistan, there was one glaring omission from his remarks -- an 'or else.' Obama's exclusion of the obvious threat -- that he will pull American troops out of Afghanistan if Karzai does not comply -- reflects a stark conundrum: How much leverage does the United States really have? 'You know that scene in the movie 'Blazing Saddles,' when Cleavon Little holds the gun to his own head and threatens to shoot himself?' asked Ronald E. Neumann, a former ambassador to Afghanistan. 'The argument that we could pull out of Afghanistan if Karzai doesn't do what we say is stupid. We couldn't get the Pakistanis to fight if we leave Afghanistan; we couldn't accomplish what we've set out to do. And Karzai knows that.' Administration officials and America's European allies say that rampant corruption and the illegal drug trade in Afghanistan have fueled the resurgence of the Taliban, and that unless Karzai moves forcefully to tackle those issues, no amount of additional American troops will be able to turn the country around. Yet many advisers to Obama, who is nearing the end of his review of American strategy in Afghanistan, said they had seen no evidence that Karzai would follow through on his promises. White House officials acknowledged that they were not planning to pull all American troops out of the country. Such a step would certainly get Karzai's attention -- it might lead to his overthrow because his political survival is dependent on the presence of American troops. But aside from the chaos it could cause in Afghanistan, officials said, a pullout could tip the balance in even more volatile Pakistan, where the government is battling Taliban militants. Senior White House officials said that they had other tools in mind, and that the new Afghan strategy would include specific goals that Karzai would be pushed to meet in areas like roads, electricity and schools, as well as corruption. The officials said they had a range of options if the targets were not met. One, they said, would be to shift money from Karzai's central government to provincial leaders who perform better than their national counterparts. And although a complete troop withdrawal is not considered an option, Obama might endorse a partial withdrawal that would lead to a more limited counterinsurgency strategy. 