Possible Clues:

• Friend based in America for a short term
• How such a word is formed initially
• Word formed of initials
• PM's predecessor entertaining friend in yuppie, perhaps
• Term initially used by mate in America
• PM isn't interrupted by chum in quango, perhaps
• America embracing ally for NATO, perhaps
• Word form
• Basis of the answer to each starred clue, commonly
• A chum married Nimby, for one