When Basel III, an international agreement between the world’s financial regulators, was announced over the weekend, initial reactions to the new capital ratio requirements — not as tough as banks had feared, but tougher than the previous accord — gave way to questions about how the agreement will be implemented.

U.S. federal banking agencies, in a press release, announced their support and endorsement of the agreement, which requires banks to more than triple the amount of high-quality capital they were previously required to set aside. The rules don’t take full effect until January 2019 (PDF), and that extended timetable has concerned some. And as Mike Konczal of the Roosevelt Institute noted, implementation of the agreement “is not a done deal.”

That last point is certainly true, if history is any indication. In 2007, the Federal Reserve announced new rules implementing Basel II, the new agreement’s weaker predecessor, but it was never fully implemented by the U.S.

Basel III, at this point, still needs to be given final approval by the leaders of the G-20, and even then it remains a non-binding agreement that needs to either be adopted into national regulations or written into law.

U.S. officials told The Washington Post they would likely try to implement the accord through new regulation, and not legislation.

That means there’s more room to tinker with the proposed rules, said Brookings’ Douglas Elliott. So depending on the intentions of U.S. regulators, it could get stronger or weaker. (A piece in the Financial Times this week suggests that in the current climate, U.S. regulators could face pressure to get tougher and, in particular, shorten the timetable for implementation.)

As it stands, there’s still the question of how much the new capital requirements will truly reduce systemic risk. In the U.S., the nation’s largest banks are already in compliance with the standards demanded by Basel III, according to the Associated Press.