Whoever, being one of the officers or employees of the United
States mentioned in section 602 of this title, discharges, or
promotes, or degrades, or in any manner changes the official rank
or compensation of any other officer or employee, or promises or
threatens so to do, for giving or withholding or neglecting to make
any contribution of money or other valuable thing for any political
purpose, shall be fined under this title or imprisoned not more
than three years, or both.