Congress has voted to override President Barack Obama's veto of a bill that would allow families of 9/11 victims to sue Saudi Arabian officials.
In the first veto override of his presidency, the Senate voted 97-1 and the House of Representatives 348-77, meaning the bill becomes law.
Mr Obama told CNN the lawmakers had made "a mistake".
The president argued the bill could expose US companies, troops and officials to potential lawsuits abroad.
CIA Director John Brennan said the vote carried "grave implications" for national security, adding: "The downside is potentially huge."
The House and Senate unanimously passed the legislation, known as the Justice Against Sponsors of Terrorism (JASTA), this year despite the Obama administration's lobbying efforts.
The bill amends a 1976 law that shields other countries from American lawsuits, allowing victims' families the right to sue any member of the Saudi government suspected of playing a role in the 9/11 attacks.
Mr Obama argued in his veto that the bill would undermine US-Saudi relations and warned of tit-for-tat lawsuits against US service members in places like Afghanistan and Iraq.
He told CNN on Wednesday: "It's a dangerous precedent and it's an example of why sometimes you have to do what's hard.
"And, frankly, I wish Congress here had done what's hard.
"If you're perceived as voting against 9/11 families right before an election, not surprisingly, that's a hard vote for people to take.
"But it would have been the right thing to do."
White House spokesman Josh Earnest told reporters the vote was "the single most embarrassing thing the United States Senate has done" in decades.
But the measure's supporters contended the legislation only applies to acts of terrorism that have occurred on US soil.
"The White House and the executive branch (are) far more interested in diplomatic considerations," said Democratic New York Senator Chuck Schumer.
"We're more interested in the families and in justice."
