At first glance, two events this week suggest that federal regulators are losing ground against “too big to fail” financial institutions. A ruling that requires the council to jump through a lot more hoops — like performing cost analyses — could slow it down considerably. That might not seem like such a big deal now, when markets appear to be relatively stable.But imagine a situation like the lead-up to 2008. A.I.G. placed huge and risky bets over a relatively short period, rapidly turning itself into a danger to the system. The council, operating under new restrictions meant to slow it down, might not be able to stop another A.I.G. before it’s too late.And then the battles over “too big to fail” would be right back where they started.