We stayed at the Mandarin Oriental in March for three nights. It was a very nice hotel and you can walk up to the national mall easily and there are several restuarants near by. Very upscale, which my daughters loved. They loved how they turned down the bed at night and left a mint on your pillow. We felt like country come to town but we enjoyed our stay. Hope this helps.
(they also had a heated indoor pool which they liked as well.)