On Tuesday, the US Senate passed a controversial bill, known as the Justice Against Sponsors of Terrorism Act (JASTA), that would allow the families of 9/11 victims to sue the government of Saudi Arabia for its alleged financial support of al-Qaeda. The bill now goes to the US House of Representatives for a vote.

The Obama administration, though, is strongly opposed to the bill and has promised to veto it, claiming it could end up putting the United States at risk of being similarly prosecuted in foreign courts.

Could it?

Critics say the administration really opposes the bill because they are trying to protect Saudi Arabia. And there is almost certainly truth to that. The US-Saudi relationship is already strained and would probably get worse if the bill were to pass. The administration believes it needs Saudi cooperation — in fighting ISIS, for example.

Still, it is worth asking whether this bill could have consequences for the US, as the administration claims. And legal experts I spoke to said that the answer is, yes, sort of, by potentially undermining a long-standing tradition in foreign relations known as "sovereign immunity."

Making it easier for the little guy to punish powerful governments for supporting terrorism

A group of 9/11 victims' families — as well as some companies who had insured businesses that were damaged in the attacks — have been trying for years to sue the government of Saudi Arabia. They allege that the country helped to finance al-Qaeda and thus should be made to pay financial damages for the group's September 2001 attacks.

But they've been unable to get American courts to agree to hear the case.

This is in large part because of a 1976 US law, the Foreign Sovereign Immunities Act (FISA), that gives foreign governments immunity from prosecution in US courts.

There are some exceptions to this immunity, but they're very narrow, and the lawyers for the 9/11 victims' families have failed in appeal after appeal to convince the courts that any of the exceptions apply in this case. The JASTA bill would widen these exceptions.

There's already a terrorism exception in the FISA, but it only applies to countries that have been officially designated by the US Department of State as "state sponsors of terror." That list only includes Syria, Iran, and Sudan — not Saudi Arabia.

This is why the family of Steven Sotloff, the American journalist who was murdered by ISIS, is able to sue the Syrian government, which they allege provided support to ISIS and is therefore partly liable for Sotloff's death.

JASTA supporters argue that the bill would widen the exceptions just enough to allow this one lawsuit against Saudi Arabia to go through.

John Bellinger, a legal advisor for George W. Bush's State Department and the National Security Council, says the bill is much broader than that.

The bill "would remove the immunity not just of Saudi Arabia but of any country in the future that commits the torts or acts of international terrorism specified in the legislation," Bellinger, who is now at the Council on Foreign Relations, told me.

In other words, the JASTA bill would make it easier for US citizens harmed in future terror attacks to sue any foreign government that they could accuse of supporting those attacks.

The bill could put the US government at risk of foreign prosecution

Critics of JASTA say that passing the bill would weaken the international norm of sovereign immunity, whereby countries block their citizens from suing foreign governments. They warn that weakening this norm could make it more likely that other countries would pass sovereign immunity exceptions allowing their citizens to sue the United States.

In a recent op-ed in the New York Times opposing JASTA, Duke law professor Curtis Bradley and Harvard law professor Jack Goldsmith, both Bush administration alumni, warned, "If the United States reduces the immunity it accords to other nations, it exposes itself to an equivalent reduction in its own immunity abroad."

"A nation’s immunity from lawsuits in the courts of another nation is a fundamental tenet of international law," they wrote. "Were the sovereign immunity rule to weaken, the United States would be subject to many more lawsuits in foreign courts than any other nation and would become an attractive and high-profile target for politicized litigation designed to contest its foreign policy."

To be clear, the concern isn't that if JASTA were to pass, Saudi Arabia would necessarily retaliate and allow its citizens to sue the American government. Nor is it the case that the global norm against sovereign immunity would likely collapse due to this one law.

Rather, the argument is more second-order: If we pass JASTA, then it will be easier to pass the next sovereign immunity exception and the next one, and eventually some countries may reciprocate. And even if the principle of foreign sovereign immunity doesn't collapse entirely, you're going to have more holes in it and thus more opportunities for the US government to get sued for its actions around the world.

"If you breach a state's sovereign immunity, then the argument against your own sovereign immunity being breached is weaker," Daveed Gartenstein-Ross, a senior fellow at the Foundation for Defense of Democracies, said.

As one hypothetical example, the Iraqi government could pass a law allowing its citizens to sue the US government for damages they suffered during the Iraq war. And if the US lost the lawsuit in the Iraqi courts, Gartenstein-Ross explained, the Iraqi government would legally be able to seize US assets in the country to pay the victims.

This is why the Saudi foreign minister told the Obama administration and Congress that Saudi Arabia would have to pull its assets out of the US if the bill were to pass, to prevent those assets from being seized in possible lawsuits against the Saudi government.

"It's actually entirely rational," Gartenstein-Ross said of Saudi Arabia threatening to remove its assets. "If Iraq passed a law saying that Iraqi citizens could sue us for things that happened during the course of the Iraq War, we would get our assets out in a second."

When is a lawsuit an act of foreign policy?

There is something else complicating this issue: For an individual to sue a foreign government is both an individual act and also an intervention into the realm of international relations, which is typically the reserve of states.

If the government of Saudi Arabia, for example, is called before a US courtroom or made to pay damages to a US citizen, then that has an impact on the foreign relations between those two countries.

Critics of JASTA warn that the bill, or any breach of sovereign immunity, thus could potentially allow individual citizens or the US judicial system the power to influence foreign policy, even unintentionally.

In our system of government, most of the power to make foreign policy decisions rests with the executive branch, with some power also given to the legislative branch.

"[I]f you think about our tripartite system of government, sovereign immunity holds that foreign policy is conducted largely, though obviously not entirely, by the executive," Gartenstein-Ross said.

"[O]f the three branches, the courts have the least ability to make foreign policy. They don't have expertise there," he went on. "Their litigation is for an entirely different reason than trying to craft good foreign policy."

This is not to say that if a foreign government supports acts of terrorism against the United States, then this government should be shielded from consequence. Rather, it's that the best way to respond is through the realm of foreign policy — economic sanctions, military retaliation — so that US foreign policy bodies can calibrate the response in a way that will best serve US interests. Allowing individuals to sue foreign governments gives up some of that control.

"From a functional perspective, the argument would be that, yes, states committing acts of terrorism is an awful thing, and in general, the way that the US should deal with that is through the executive undertaking its foreign policy, as opposed to US citizens suing that state in an American court," says Gartenstein-Ross. "It’s something that we prefer the executive to deal with, as opposed to citizens suing in court, independent of any sort of foreign policy imperatives."

While families of terror attack victims have every reason to want to punish a country they believe supported that attack, that may not necessarily be in the best interests of the United States — particularly given doubts, in this particular case, that the foreign government in question is actually guilty.

Making it easier for individual US citizens to sue foreign governments risks introducing a degree of chaos into the foreign policy decision-making process, undermining the ability of the president and the others we've collectively decided as a country to task with such things to craft careful, informed foreign policy on behalf of all Americans.