With the one-year anniversary of last year’s Wall Street reform bill fast approaching, a debate is brewing about whether the measure is capable of achieving one of its signature goals: ending government support for financial firms that are “too big to fail.”

Taxpayers saw “too big to fail” play out in September 2008, when the Federal Reserve authorized an emergency $85 billion loan to insurance giant AIG to prevent the fallout its “disorderly failure” might have had on financial markets.

To prevent a repeat of history, the Wall Street reform bill, signed into law by President Obama on July 21, 2010, contained an explicit ban on future AIG-style bailouts: “No taxpayer funds shall be used to prevent the liquidation of any financial company,” the law says.

So it is not surprising that when Rep. Barney Frank (D-Mass.), one of the law’s chief architects, spoke this week in front of the National Press Club to reflect on its progress one year later, he insisted several times that “too big to fail” was over:

“We are the first nation to say, ‘Hey, if you get in trouble, you're dead.’ And we will then worry about your mess, and we may have to minimize the mess you left behind. But if we — if that costs us any money — it's coming from your colleagues; it's not coming out of the taxpayer. And we think that model is an attractive one.”

But whether that model will work in practice is a whole other issue. John Walsh, acting comptroller of the currency, said in a June speech that banks’ “unique role” in the economy “requires them to take risk,” and therefore “justifies the maintenance of a public safety net” by taxpayers, which is “unlikely ever to be provided at zero public cost.”

The remark earned him a reprimand from Frank: “As you know, the financial reform law passed last year closes off that possibility,” Frank wrote to Walsh in a letter July 12. “I would appreciate your dispelling this notion immediately so that taxpayers and market participants are confident that the U.S. government stands firmly behind the idea that the era of bailouts is over.”

But with Frank’s signature on the letter still fresh, another challenge has emerged. Standard & Poor’s, a major credit rating agency, released a report the same day last week arguing that Frank’s law doesn’t end “too big to fail.”

“Under certain circumstances and with selected systemically important financial institutions,” Standard & Poor’s concluded, “future extraordinary government support is still possible.”

“I would suggest that you reconsider your apparent decision to diversify into legislative analysis and political prognostication,” Frank wrote to Standard & Poor’s President Deven Sharma in response to the report.

As regulators carry on with the task of setting in place rules implementing Frank’s Wall Street reform bill — and lobbyists continue their efforts to water it down — it is likely that exchanges like these will only become more common.