Unfortunately, 100% of the Congress chose to accept Obama as eligible, even though through unidentified proxies (with potential future deniability) he stipulated that the children of his father were governed by the 1948 BNA.
This was, in my opinion, an unconstitutional defacto amendment of the constitution, but the matter has never properly come before SCOTUS for a definitive ruling as to what NBC means specifically for Obama.
For this SCOTUS review to occur, his original records must actually be subjected to discovery and challenge in court including witness testimony and international document authentication regarding any evidence that Obama was not born in HI or was adopted or expatriated and held Indonesian passports and citizenship.
I would contend, that a very large majority of Congress had no clue that Barry was born the subject of a foreign crown. Heck, most of them have no clue as to the difference between a "citizen" and a "natural born citizen" as evidenced by their reply's to inquires about Barry's eligibility.
As for the others, I believe that this all boils down to his race. There was not a single person in Congress (or in the "big" media/radio) that was going to go out on a limb to try and expose the first "black" POTUS...even though he's more white and arabic than black. He simply wasn't going to be denied, especially in light of his high popularity ratings both before and right after the election.
Of course, the tide may eventually turn. Think in terms of the Nixon timeline.