Not a lot of options
Hi Richard. I've was a lurker at Gail's for longer than I care to remember, and only just found this place about a week ago. Would never miss the opportunity to help out someone coming to DC.
I work across the street from Union Station and a few blocks from the Capitol. You don't have too many great options for a business dinner (or any dinner for that matter), but here are some options.
Charlie Palmer's Steak House. I haven't been there, but hear pretty good things about it. They actually present their wine list on an iBook! Probably your best chance to spot some politicos.
Bisto Bis in the Hotel George. Not as good as it it once was, IMO, but still quite good and very lovely.
B. Smiths in Union Station. Upscale Southern cuisine. Food is not great, but the setting is gorgeous.
And depending on when you are visiting, Johnny's Half Shell will be relocating from Dupont Circle to Capitol Hill (site formerly occupied by La Colline) sometime in late July. Date is not set yet, but that's what they're shooting for. In the spirit of full disclosure, I am good friends with the owner but will strongly endorse this excellent restaurant.
That's pretty much it for that area, that I can recall. Good luck!