The only real limit on how the next president employs drone strikes appears to be whatever rules they choose to set for themselves.

President Trump’s decision to kill Iranian General Qasem Soleimani on January 2 was far from the first time that an American President has used a drone strike to kill a foreign target on foreign soil. In January 2009, just a few weeks after taking office President Obama authorized the first lethal drone strike of his presidency. That strike, which occurred in Pakistan, reportedly missed its primary al Qaeda target but did kill five other militants and between 9 and 11 civilians.

Over the next eight years, hundreds of drone strikes were authorized by Obama, mostly in Pakistan, but also in Yemen and Somalia. Military drone strikes were also conducted in Iraq, Afghanistan, and Syria.

Since taking office Trump has escalated the use of CIA drones for targeted killing in these countries, ordering hundreds of strikes and continuing the use of drones as part of ongoing military operations.

Looking at how the two presidents have chosen to use drones or unmanned aerial vehicles to conduct lethal operations can help clarify what, if any, are the current functional limits of presidential power regarding this technology.

When, if Ever, Are Drone Strikes Considered Legal?

Drones have become an important part of the U.S. military arsenal and determining when and how they can be used can come down to complicated legal questions about who exactly the U.S. is at war with and where that war is taking place.

Both President Obama and President Trump have ordered strikes using drones operated by the military and the CIA. Because the “War on Terror” is against non-state actors like al Qaeda and ISIS that don’t operate within national borders, the geographic limits of that war are hard to define.

According to the U.S. Constitution, only Congress has the power to declare war. But whether a drone strike or targeted killing is considered an act of war is a murky issue at best and both Obama and Trump have chosen to bypass congressional approval when ordering drone strikes.

Some give drone strikes legitimacy when conducted with the approval of the local government, which at times the U.S. has been granted. Pakistan is one of America’s closest allies. U.S. personnel often work closely with the Pakistani military, including on operations, using drones. Yemen has been in the grips of an ongoing civil war since 2014 and lacks a cohesive functional government yet the U.S. has backed a Saudi Arabian-led coalition in the conflict and conducted drone strikes against al Qaeda and other targets in Yemen since 2002. A recent resolution to end U.S. involvement in Yemen passed the House but not the Senate. In Somalia, recent drone strikes have been in coordination with the Somali government.

The Pentagon and President Trump have justified Soleimani’s killing by linking him to attacks on coalition bases in Iraq and the December 31 mob attack on the U.S. Embassy in Baghdad. The Trump administration also claimed Soleimani posed an imminent threat to the U.S. and was planning a pending attack.

“General Soleimani was actively developing plans to attack American diplomats and service members in Iraq and throughout the region,” the Department of Defense said in a December 2 statement. “This strike was aimed at deterring future Iranian attack plans.”

However, the U.S. has offered no proof that Soleimani was planning an attack and Iraq says Soleimani was in the country to engage in diplomatic efforts. These and several other factors are calling into question the legality of the U.S. strike on Soleimani and have focused international attention on it in a way that Trump’s previous use of drones up to now has avoided.

For one thing, the U.S. military operation in Iraq officially ended in 2011, but the legal presence of several thousand U.S. troops has been maintained at the invitation of Iraq’s Prime Minister with the stated purpose of assisting Iraq’s military to fight ISIS. Soleimani was also in Iraq at the invitation of Iraq, again supposedly for peaceful purposes. Additionally, Soleimani was an Iranian General, part of the nation’s military force, not a member of a terrorist organization although the U.S. designated the elite Iranian Quds Force a terrorist organization by executive order in 2007. The U.S. operation was also conducted in Iraq apparently without the knowledge or approval of the Iraqi government.

Whether or not Soleimani’s death meets the criteria of an act of war or whether the region and/or the U.S. are safer without him as a threat is being debated. What does seem clear is that this particular use of a drone to kill is outside the previously established parameters of how drones have been used.

Accountability and Transparency

There have been conflicting accounts of when and how much Obama knew about the civilian deaths caused by his first drone strike. However, as he continued to choose to use this technology for lethal ends it’s clear that he was aware that civilians were dying.

In 2013, Obama created what was referred to as the drone “playbook.” The document included rules about who could be targeted by drones, where and with whose approval. It also set limits on the acceptable number of civilian casualties. It’s not clear how these limits or other rules of the playbook were monitored or enforced while Obama was in office.

There was also no apparent mechanism to ensure that future Presidents would adhere to these guidelines. In March of this year, President Trump signed an executive order to end the requirement to report civilian casualties of drone strikes, and the President is reportedly working on drafting a new playbook for drone use.

Obama Drone Strike Precedent and Aftermath

Obama’s efforts to tighten the rules about drones may have been intended to set a path towards more circumspect use of deadly force, but it seems to have created a precedent where each president gets to set their own rules. Trump has demonstrated that he feels largely unconstrained in what he is allowed to do as Commander in Chief, and this clearly extends to his authorization of drone strikes in or out of war zones.

Questions about the legality of Soleimani’s death and how Trump has used drones may soon be eclipsed by the larger fallout from this incident if it leads to a major international conflict. Drones will inevitably play a military role in that conflict and continue to be a part of how U.S. leaders deal with perceived threats around the world. The next president will have this same technology at his or her disposal and at this point the only real limits on how they can use it appear to be whatever rules they choose to set for themselves.