U.S. Congress vs United States Congress

U.S. Congress and United States Congress both are nouns.

Word	Noun	Adjective	Verb	Adverb
U.S. Congress	Yes	No	No	No
United States Congress	Yes	No	No	No

As nouns, U.S. Congress and United States Congress are synonyms defined as:

U.S. Congress and United States Congress: the legislature of the United States government

Other synonyms of U.S. Congress include Congress, US Congress.

U.S. Congress (noun)	United States Congress (noun)
the legislature of the United States government	the legislature of the United States government