Does the bar of res judicata operate against the taxpayer as well as the tax collector?

9 As Pope Estate noted, the bar of res judicata may operate against the taxpayer as well as against the tax collector. In Guettel v. United States (8th Cir.1938) 95 F.2d 229, the taxpayer had successfully brought an action for refund of a portion of his federal estate tax, claiming that certain items should not have been included in the estate. He later brought a second action, claiming that certain real property as well should not have been included in the taxable estate. This second action was held barred by the judgment in the first.