Correct me if I'm wrong here, but when indicating possession for a plural word that ends in 's', you add an apostrophe after the last 's', and do not add an 's' after that apostrophe (i.e. the possessive of kids would be kids'). Therefore would "Congress's power" have been more correctly written "Congress' power"? I'll throw out there that I may be constructing it incorrectly (as Congress') because 'Congress' may, in fact, be a singular noun (in this case) which would require the 's construction. Oh English
As far as I can see, "Congress" is a singular noun with plural "congresses" (and a somewhat archaic verb too, of course).
A plural noun ending iin s simply appends an apostrophe. A singular noun ending in an s sound used to be converted to the possessive the same way. For some nouns, that practice continues, but increasingly the rule is shifting toward appending 's; As digitig points out, Congress is actually a singular noun. so Congress's foibles is now slightly preferred. But you would still freak when you saw the mess in the boys' bedroom.
O.k. congress and mess in boys bedroom does not belong in the same sentence...well, I guess it could belong, but only if there is protection involved. And why am I stuck thinking the archaic definition of this word?
Good to know. I guess I was slightly incorrect in my expectation of Congress's construction. Bah, that still looks wrong to me.
Well, at least it's a lot less work to learn that "congress" is singular than it would be to re-learn how to construct English possessives ;-)