If the bank failed prior to October 3, 2008, then you can't claim $250,000 coverage (12 CFR sec 330.1(n)).
That said, the only argument that would seem to fit the facts would be that the federal government has demonstrated administrative negligence, in its general management of the investment banking community, and "but for" that negligence your banking instution would not have failed. The most pervasive example of this negligence is the SEC's almost categorical failure to investigate claims by various sources into Madoff Investments. While this does not show a direct link to the failure of IndyMac, the SEC undoubtely failed similarly to regulate deriviative trading in mortgage securities, and that failure should be imputed to the Dept. of Treasury, which controls both the SEC and FDIC.
This is more than a policy failure. It shows that investigaton simply did not occur, regardless of the government's general mandate to regulate the investment and banking community.
What I'm getting at here is trying to make this a much bigger deal. Government is immune from making stupid policy decisions, but not from the failure to actually do what policy instructs. So, if you can show an endemic failure to regulate what the government was required by Congress to regulate, then you have a huge negligence action against the government that cannot be avoided under the doctrine of sovereign immunity.
This would also be extremely scary to government regulators, and they might just pay you to shut up and go away.
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