The death of Afghan Taliban leader Mullah Mansour in an American drone strike is a significant but not fatal blow to both the Taliban and their Pakistani Army patrons.

The critical question Afghans and Pakistanis are asking is whether this is a one-off or the beginning of a more aggressive American approach to fighting the war in Afghanistan.

Mullah Mansour became the Taliban's leader last year after it was revealed his predecessor, Mullah Omar, the founder of the Taliban, had been dead for two years from unknown causes.

Mullah Omar's death in a Pakistani hospital in Karachi had been covered up for two years by the Pakistani Army's intelligence service, the Inter Services Intelligence Directorate or ISI, and the cover-up allowed the ISI to manipulate the Taliban very effectively behind the scene. Mullah Mansour was the ISI's handpicked successor.

There was resistance to his selection by some Taliban commanders, but the ISI forced them to acquiesce.

Since the fall of Kabul to American and allied forces after 9/11, the Taliban leadership has made its headquarters in Quetta, the capital of Baluchistan province in Pakistan.

For 15 years the Quetta Shura, as the assembly of leaders is known, has been protected by the ISI in its Pakistani safe haven where it is free to plan operations, conduct training, raise money and prepare terrorist attacks to strike American, NATO and Afghan targets in Kabul and elsewhere. While drones pummeled Al Qaeda targets elsewhere in Pakistan, the Taliban leaders were immune.

So this operation is unprecedented, the first ever effort to decapitate the Afghan Taliban. Mullah Mansour apparently was killed in Baluchistan very close to the Afghan border. He pressed his luck too far it appears. It's too soon to know the details of how he was found, but he was likely visiting front-line commanders.

The ISI will find a successor. They will work with the powerful Haqqani network, inside the Taliban, which has its own sanctuary in Peshawar Pakistan. The challenge will be to hold together the fractious movement, especially as the so-called Islamic State (ISIS) is trying to rally dissidents to its cause and create an Islamic State Vilayet, or province, in Afghanistan. The ISI and the Haqqanis are prepared to be ruthless to keep control of the Taliban.

The elected Pakistani government led by Prime Minister Nawaz Sharif has been trying to persuade Mullah Mansour and the Quetta Shura to join in peace talks with the Afghan government, which is led by President Ashraf Ghani. The US and China have encouraged the political process. But Sharif has no power over the Pakistani military and its ISI minions.

Indeed, now that Prime Minister Sharif is engulfed in a scandal caused by the Panama papers, his goal is simply to survive in office, and some Pakistani political commentators expect the army to oust Nawaz Sharif in a soft coup this summer. The Afghan peace talks are not likely to get going as long as the army calls the shots in Pakistan.

The killing of Mansour in an unprecedented operation has produced elation in the Afghan security forces, who hope it does it actually does mark the start of more aggressive attacks against the safe havens in Pakistan. But that's probably a misplaced hope. A discreet operation in the border region is not the equivalent of hitting targets deeper inside Pakistani territory.

Inevitably, the attack will be another blow to U.S.-Pakistan relations, even if both Washington and Islamabad try to paper it over. The U.S. Congress, after years of passively accepting Pakistani duplicity, has become much less willing to fund arms deals and aid to the Pakistani army. A recent administration proposal to sell F16 jets to the Pakistani military at sweetheart prices has been killed, wisely, on The Hill.

The next U.S. president will confront a complex and worrisome challenge in Afghanistan and Pakistan. It is not quite as bad as the disaster President Barack Obama inherited eight years ago, but it is one of the toughest foreign policy issues the next team will face. What do the candidates think they can do about it? It's not too early to start pressing them for answers.