Question

A foreign policy fail that president carter achieved was ?

Answer 1

... not being able to free American hostages taken by Iran.

President Jimmy Carter’s failure to get the hostages back ruined his re-election chance in 1980.  We might also want to note that the taking of the hostages was the result of a foreign policy mistake by President Carter.  The Iranian Revolution had ousted the shah of Iran, a US-backed leader.  The former shah, Mohammad Reza Pahlavi, living in exile in Mexico, was found to have cancer, President Carter allowed him to come to the United States for treatment.  This enraged the Iranians, who thought that the US was perhaps trying to bring the shah back to power.  That's when the hostages were taken.

Answer 2

not being able to bring home the Iranian hostages.