As early as this week, the House and Senate could deliver the first veto override of Barack Obama’s presidency, with supporters of legislation crafted to allow 9/11 victim families to sue Saudi Arabia pushing back against claims it would upset international legal norms.

The Justice Against Sponsors of Terrorism Act would authorize lawsuits against foreign governments who “knowingly or recklessly,” “directly or indirectly” contribute material support to people who commit acts of terrorism within the United States.

The bill passed both chambers of Congress without opposition and is supported by the Democratic and Republican presidential candidates. Advocates say it’s necessary to deter and punish countries that sponsor violent extremists and an advocacy group pushing for passage offered a comprehensive rebuttal of Obama’s veto message.

Opponents including many scholars, ex-officials and the White House, however, say it could harm the U.S. by disestablishing reciprocal sovereign immunity, a legal principle that generally protects governments from being sued in a foreign country’s legal system.

Because it initially passed in voice votes, it’s unclear if there are enough support to override the veto, which requires two-thirds backing in each chamber. But things are moving quickly with lawmakers anxious to return home for a pre-election October recess.

David Popp, a spokesman for Senate Majority Leader Mitch McConnell, R-Ky., says the Senate will vote on the potential override Wednesday at a time yet to be determined.

The House of Representatives won’t act until the Senate does, but it will remain in town as late as needed, says a spokeswoman for House Speaker Paul Ryan, R-Wis.

“We can't take it up until the Senate acts -- it's a Senate bill,” explains AshLee Strong, a spokeswoman for Ryan. She adds: “The House won’t leave without acting."

There’s substantial disagreement on the stakes of the bill, which unites centrist party leaders with lawmakers habitually critical of the U.S. alliance with Saudi Arabia. Defenders of the bill, such as Democratic Sen. Chuck Schumer of New York, argue it’s narrowly tailored and that Saudi Arabia has nothing to fear if it’s innocent of involvement in 9/11.

Notre Dame University law professor Jimmy Gurule, who supports the bill, says JASTA critics exaggerate concerns about other countries retaliating with rollbacks in their own sovereign immunity laws and says the bill’s requirement that the terrorist attack happened within the U.S. limits the number of potential lawsuits.

Gurule says sovereign immunity has never been absolute anyhow. Earlier revisions allow lawsuits if a state is acting like a business, or for certain non-commercial reasons if an offense occurs entirely within the U.S. In 1996 Congress passed legislation allowing lawsuits against State Department-designated state sponsors of terrorism.

Unlike the 1996 legislation, JASTA would only authorize lawsuits over acts of terrorism committed within the United States, and it allows the State Department to press pause on litigation if it asserts there are good faith negotiations with a defendant country.

Gurule says although there have been large financial judgments against Iran -- about $53 billion, with the Supreme Court ruling in April that $1.75 billion of cash seized from Iran's Bank Markazi could go toward victims -- there hasn’t been much retaliation.

Some countries that have been on the short list of U.S. adversaries on the state sponsors of terrorism list, such as Sudan, have rudimentary court systems, Gurule says, but others also haven't struck back.

“You don’t see Syrian citizens rushing to the courtroom," he says. “My view is these arguments -- of retaliation, reciprocity and legal chaos -- are really an attempt to conceal the real reason for the White House opposition to JASTA, and that is simply that the United States feels this legislation would strain relations with Saudi Arabia."

Countries with productive relations with the U.S., such as oil-producing Angola, where the U.S. funded a murderous rebel group for decades, or Vietnam, the U.S. bomb freckled manufacturing-exporter, would not respond to JASTA with lawsuits, Gurule says, because the U.S. carries a big stick -- be it trade incentives, foreign aid or mere diplomatic weight.

There currently is a narrow exception to sovereign immunity for lawsuits against countries over crimes in the United States. Chile, for example, was sued after the government of dictator Augusto Pinochet murdered a dissident Orlando Letelier and another person with a car bomb in Washington, D.C., in 1976.

But that exception isn’t applicable to the 9/11 attacks because of the skimpier public evidence of direct state involvement.

"If the Saudi ambassador carried a bomb with him into the State Department and blew up the State Department.... I would say that's the same as the Chilean car bombing,” says Columbia University law professor Lori Damrosch. "Basically all elements of the tort would have to happen in the U.S. [With 9/11] it's a little more complicated."

Damrosch says she worries that the “directly of indirectly,” “knowingly or recklessly” wording of JASTA might ensnare governments with tangential connections to terrorism.

"That means a reckless Saudi paymaster of some sort who indirectly allowed funds to be transferred to someone who used them for terrible purposes would allow lawsuits to be brought against Saudi Arabia itself," Damrosch says.

Gurule, however, says that ultimately Saudi Arabia would not be found liable except for if truly damning evidence emerges.

“In tort law there must be causation, so the conduct that’s the subject of the litigation… must be the proximate cause of the injury… there must be a direct nexus between the state’s conduct and the resultant death or injury,” he says.

The current public record on Saudi Arabia’s connection to 9/11 hijackers, 15 of 19 of whom were Saudis, appears to indicate some contact, but publicly released records such as the long-withheld 28 pages of initial congressional investigative notes on Saudi connections -- released earlier this year, don’t reach that threshold.

Victim families, who protested at the White House before Obama’s veto, say they believe court proceedings could turn up additional evidence.

Some family members worried that Obama took the full 10 days allowed for a presidential veto to run out the clock on the current congressional session -- though an alternate theory holds the White House wanted the maximum among of time to survey and twist arms in Congress.

Saudi Arabia has warned that it may have to sell off $750 billion in U.S. assets if JASTA passes. Some scholars, such as University of Virginia law professor Paul Stephan, who opposes the legislation, says it's not clear to him that many Saudi assets -- possibly held under a sovereign wealth fund -- could be targeted.

Stephan says he lacks the faith advocates of JASTA place in the civil legal system as a route for to punish state-sponsored terror. He says military action is more appropriate, though he acknowledges, "some would argue the Saudis have bought up all of the U.S. government and we can't really trust the executive branch to vigorously investigate the Saudis, and that's why we need private lawsuits to get at the truth."

Gurule, a former assistant U.S. attorney general and under secretary for enforcement at the Treasury Department, says even if JASTA becomes law it's unlikely the Saudis will be on the hook -- unless truly damning evidence emerges.