The federal government can run out of money

No. Article 1, Section 8, of the U.S. Constitution gives Congress the authority to create money and establish its value. There are no limits on its ability to create money. As described elsewhere, there are real, practical limitations on how much it should create at any given time. However, it is nonsensical to ever say that the federal government cannot find any dollars or that the federal government is broke. If you had a magic checkbook that never ran out of checks and whose checks never bounced, you could never run out of money, either.