The Islamic State has conquered broad swaths of Iraq thanks to a surprising alliance with secular veterans of Saddam Hussein’s military. But now that partnership is fraying — giving Washington its first real opportunity to blunt the terrorist group’s advance without relying solely on American airstrikes or ground troops.

The group of ex-Hussein loyalists, known alternatively as the Naqshbandi Army or by the acronym JRTN — the initials of its Arabic name — helped the Islamic State, formerly known as ISIS, win some of its most important military victories, including its conquest of Mosul, Iraq’s second-largest city. It has also given the terrorist army, which is composed largely of foreign fighters, a valuable dose of local political credibility in Iraq. JRTN, which was formed as a resistance group in 2006, is made up of former Baathist officials and retired military generals, and is led by the former vice president of Hussein’s revolutionary council, Izzat Ibrahim al-Douri, who was once one of the most-wanted men in the country during the U.S. occupation.

ISIS and JRTN aren’t natural allies. The former wants to erase Iraq’s current borders and establish a caliphate, while the latter has been a largely secular movement that seeks to regain the official power and influence it held before the U.S. invasion in 2003. But they are aligned in their opposition to, and hatred of, outgoing Iraqi Prime Minister Nouri al-Maliki’s Shiite-dominated government. Each side wants him to go, and JRTN recognizes that ISIS stands the best chance of violently overthrowing the Iranian-backed regime in Baghdad.