One year into his long presidential tenure, U.S. President Franklin D. Roosevelt established relations with the Soviet Union. The U.S. at the time said it received pledges from Moscow to respect religious freedoms, to halt support for communist groups in the U.S., and to open talks on settling pre–Soviet era Russian debts. In practice, little changed, and the relationship quickly soured, though the two nations never severed diplomatic ties again.
Since the USSR didn't keep its promises, why did the US maintain diplomatic relations with them?