Congress seems determined to set a new standard for craven incompetence. Less than 24 hours after the Senate and House delivered a stinging rebuke to President Obama by overriding his veto of a bill that would let the Sept. 11 families sue Saudi Arabia, Republican leaders raised the possibility of a do-over.

On Thursday the Senate majority leader, Mitch McConnell, said that “nobody had really focused on the potential downside in terms of our international relationships, and I think it was just a ball dropped.”

It’s rare to hear such a baldfaced admission of gross ineptitude. But instead of putting the responsibility entirely where it belongs — on Congress — Mr. McConnell went on absurdly to blame Mr. Obama for failing to communicate the potential consequences of the bill. In fact, Mr. Obama, the national security agencies, the Saudi government, retired diplomats, the European Union and big corporations had all bombarded Congress with warnings. Yet lawmakers ignored all of them in a rush to pass the legislation and then, this week, override Mr. Obama’s veto by a large bipartisan vote.

The new law would allow families of the victims of the Sept. 11 attacks to sue Saudi Arabia for any role it had in the terrorist operation. It would do that by expanding an exception to sovereign immunity, the legal principle that protects foreign countries and their diplomats from lawsuits in the American legal system.