Are big, ugly, taxpayer-funded bank bailouts a thing of the past in the U.S.? Moody's Investors Service seems to think so. The Government Accountability Office isn't so sure.

Yesterday evening, Moody's announced that the credit ratings of the eight largest U.S. bank holding companies -- JPMorgan Chase & Co., Bank of America Corp., Citigroup Inc., Wells Fargo & Company Inc., Goldman Sachs Group Inc., Morgan Stanley, State Street Corp. and Bank of New York Mellon Corp. -- will no longer receive any "uplift" thanks to the expectation of government support in times of trouble. The move comes at an opportune moment for the banks, which, as Bloomberg View wrote in a recent editorial, have been seeking to avoid tougher capital rules by arguing that the government can safely let them fail.

Moody's says it is convinced that, next time a crisis hits, the government will impose losses on banks' creditors instead of using taxpayer money to make them whole. The primary reason for the credit-rating company's newfound confidence is a piece of the Dodd-Frank Act known as the orderly liquidation authority. It gives the Federal Deposit Insurance Corp. the power to swoop in and take over a struggling bank holding company, keep all the important operating subsidiaries running, and restore the whole thing to solvency by turning creditors into equity holders.

Interestingly, the Moody's announcement came on the same day the GAO issued a report with a very different perspective. As part of a broader examination of the government support provided to banks during the 2008 crisis, the report listed some serious concerns about the liquidation authority.

Regulators, for example, might balk at forcing losses on creditors, for fear of triggering a broader crisis. In the case of large, multinational banks, the FDIC might not be able to coordinate its actions with other countries'. Most important, a 2008-like systemic meltdown could overwhelm the FDIC. The GAO cited a survey of investors in which "few respondents believed that FDIC could effectively use OLA to handle the resolution of multiple firms simultaneously."

Whom should we believe? Well, first consider that over the past few decades the government has almost always rescued big banks in distress, for fear that a major failure would sink the economy -- a fear that the disastrous bankruptcy of Lehman Brothers Holdings Inc. only reinforced. The country's biggest banks, as a group, are even larger now than before the crisis and no less systemically important than in 2008 and 2009, when the government last saved them. Even the FDIC's own vice chairman, Thomas Hoenig, has said that the liquidation authority couldn’t handle a systemic meltdown -- meaning that the government would have to step in with taxpayer money.

Now think about the incentives that Moody's and the GAO face. The biggest U.S. banks are some of the credit-rating company's largest paying customers. According to a U.S. Senate report, Moody's has responded to bank pressure in the past, by putting its triple-A stamp of approval on many of the mortgage investments at the center of the last financial crisis. The sole mission of the GAO, by contrast, is to investigate the use of public funds. Its clients are the lawmakers who asked for its assessment of past and potential government support to banks.

It certainly would be pleasant to believe that Dodd-Frank has solved the problem of banks that are so big and systemically threatening that the government can't let them fail. Unfortunately, the leap of faith required is still too great.

(Mark Whitehouse is a member of the Bloomberg View editorial board. Follow him on Twitter.)