Congressmen being full of hot air is not a recent development.
In 1820, Rep. Felix Walker, who was from Buncombe County, N.C., gave a long, rambling speech in the U.S. House. Not much was remembered about it other than it had little relevance to that day’s business.
Walker, originally from West Virginia, became known for using the expression “speaking for Buncombe.” This quickly got modified and was used to label any kind of nonsense or questionable statement. It was called “bunkum” and then later, “bunk.”
You can get more details on the story from the N.C. Department of Cultural Resources page here.