Slippery slope limiting America's support (8)
I believe the answer is:
espousal
'support' is the definition.
(thesaurus)
'slippery slope limiting america's' is the wordplay.
'slippery' is an anagram indicator (I've seen this in other clues).
'limiting' indicates putting letters inside.
'america' becomes 'usa' ('U.S.A.' can be a synonym of 'america').
'slope' with letters rearranged gives 'espol'.
'espol' going around 'usa' is 'ESPOUSAL'.
(Other definitions for espousal that I've seen before include "championship" , "old-fashioned marriage" , "Acceptance with approval" , "Adoption (of a cause) - USA's pole (anag)" , "Action of adopting (a cause)" .)