The success of American efforts in Afghanistan has always hinged on a critical variable—whether neighboring Pakistan abandons its strategic hedging and comes full-bore against the Afghan Taliban.

That hasn’t happened in the past 16 years despite exhortations by successive American administrations. Such a shift appears just as unlikely now, even after President Donald Trump’s forceful appeal on Monday “for Pakistan to demonstrate its commitment to civilization, order and peace.”

While providing logistical support to the U.S.-led coalition in Afghanistan, Pakistan’s security establishment—despite official denials—has also long nurtured elements of the Afghan Taliban, particularly the Haqqani network, according to U.S. officials. Many of Pakistan’s generals and spies have described the Afghan Taliban, as distasteful as they may be, as a useful tool against an existential enemy that already dismembered their country once—India.

It’s this doctrine of Afghanistan as “strategic depth” versus India that has prompted Pakistani intelligence to back the rise of the Afghan Taliban all the way since the 1990s, according to U.S. officials. Even now, the fear that India may use Afghanistan as a backdoor to destabilize Pakistan remains a key factor in Islamabad’s geopolitical calculations.

Already, Pakistani officials blame Indian saboteurs operating out of Afghanistan for fanning the separatist insurgency in Pakistan’s Baluchistan province, an allegation denied by New Delhi. Afghanistan has long refused to recognize its border with Pakistan, and many Pakistani officials worry that a stable Afghan government allied with India could aggressively pursue those territorial claims.