Grassley has asked TARP inspector general Neil Barofsky to investigate the deal. Among the questions he posed in a letter to Barofsky is whether "the acquisition of AmeriCredit at the price paid by GM will increase the likelihood that the American taxpayer will recover more of its money from GM than currently estimated."

Willens thinks it will. He points out that an additional benefit to GM from the deal is that AmeriCredit will be able to kick the amount it saves on taxes up to GM.

"I think this is a good deal for GM and a good deal for taxpayers, since they after all are GM shareholders," Willens says.

However, he concedes the Treasury will lose tax revenue from AmeriCredit if it weren't able to use GM's losses to shelter its earnings.

"It depends what the goal is; whether to increase overall tax revenues or to get paid back on the GM investment," Willens says.

Also, as Steven Davidoff pointed out in The New York Times' DealBook , a GM acquisition of Ally Financial, the former GMAC, might have given the government a better chance of recouping its $17.6 billion investment in that institution, which Davidoff argues "looks more at risk." In other words, what's good for GM isn't necessarily good for the government--notwithstanding taxpayers' 60% stake in the automaker.

If the AmeriCredit deal gets done over the concerns of Grassley and others, it could open the floodgates for a host of similar acquisitions by companies that took some of the biggest losses during the financial crisis. As TheStreet pointed out in June, many companies, including GM rival Ford Motor Co. ( F), are in a situation similar to GM--with big net operating losses but without enough earnings power to make full use of those losses to offset taxes.

Some of those companies, such as Citigroup, AIG and of course Fannie Mae (FMCC.OB) and Freddie Mac (FNMA.OB) are still largely owned by taxpayers as GM is. If GM can get its deal through, other potential acquisitions that seemed far-fetched may suddenly appear less so.

One factor that may help GM sell its deal to regulators and politicians is that fact that AmeriCredit, which makes car loans, is a business closely related to GM's. It probably wasn't necessary, however, in the view of Willens. Earlier this year, a former software company called Clarus Corp. ( BDE) bought a pair of outdoor sporting goods companies in order to take advantage of its tax credits from losses accrued several years earlier.

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