In De Simone v. United States, the petitioner, a naturalized U.S. citizen originally from Italy, was convicted of conspiracy to violate federal narcotics laws and sentenced to five years in prison. The government then sought denaturalization on grounds that he had concealed his criminal history during the naturalization process. The Supreme Court held that since De Simone's conviction occurred after his naturalization proceedings were completed, it could not be used as evidence of bad moral character at the time of those proceedings or as proof that he lied about having good moral character during them. Therefore, they ruled against revoking De Simone’s citizenship because there was no clear and convincing evidence proving fraudulent concealment or willful misrepresentation at the time when he applied for citizenship.

In the dissenting opinion for De Simone v. United States, it was argued that the majority's decision failed to properly consider and apply principles of equity. The dissenting justices believed that De Simone should have been allowed to withdraw his guilty plea due to a misunderstanding about its consequences. They pointed out that he had pleaded guilty under the impression he would be deported back to Italy, which did not happen because deportation proceedings were suspended indefinitely by immigration authorities. This left him in a state of legal limbo with no end in sight - an outcome he could not have foreseen when entering his plea. Thus, they felt this constituted "manifest injustice" warranting relief from his conviction under Rule 32(d) of Federal Rules of Criminal Procedure.