What is this K Street you speak of, if you don't mind my asking? I've not heard that turn of phrase before.

If I had to guess it's a name given to the phenomena by which what a freshly elected legislator ends up doing once they get to Washington D.C. tends to differ from what they actually get to do based on having to grapple with the political realities at the National level. This would include exposure to well funded lobbyists as well.

But that's just a guess...