If you get tickets for Ford's Theater, try Bistro D'oc. It's not as fancy as any of the others, and is a bit Euro-bohemian, but I have consistently great dinners there. For fancier, over there, I think Jose Andres Minibar only takes reservations a month out, so that could be worth a try. The outside bar at, I think, Poste Modern, has fluffy blankets, fire pits and adult cocoas, which could be quirky fun for a romantic evening.

Those are all a couple block walk from the Willard. Closer by, I've really enjoyed Ceiba. I don't do dinners at Old Ebbitt but I do like to stop by for a martini and a plate of oysters after theater, if we're in that part of town.

I've always thought La Chaumiere in Georgetown looked uber-romantic but have never actually been.

If the theatre is Ford's, Bistro d'Oc, right across the street, is nice. (And Old World--specifically, SW France)

J&G Steak
Oval Room--a bit of a walk, but the walk is through Lafayette Park in front of the White House.
701 is also nice. A bit of a walk in the other direction--down Pennsylvania, toward the Capitol.

How about Founding Farmers or Rasika West End?

Cafe du parc, equinox, or DC coast.

West end bistro

J&G Steakhouse and Tosca are both close and good. Proof is farther and more modern style, but just had a great meal there last weekend so I thought I'd mention it.

The Occidental

DH and I have a weekend stay at the Willard while the grandparents have the little one. Would like to make reservations for dinner Saturday evening somewhere close to the Willard or a local theatre (if we can get into a show). Short notice so no 1 month + waits, but I want a reservation so we don't have to wait when we get there. Cost is no object, but cheap is fine too if it's romantic! Prefer old world to modern/trendy, but not totally opposed if the food is great and atmosphere is romantic. We've done Petits Plats, 1789, Nora in the past, all great but would prefer to try something new. Thank you!