Congrats go to Tillerman! I think that may have been the fastest he ever gave me the correct answer, which he attributed to a hunch and blind luck.
Yes, it is the infamous Washington Hilton, the same place where — on a Monday at the end of March, 1981 — President Ronald Reagan, just 69 days into his presidency — was struck by an assassin’s bullet and nearly killed. In fact, it’s in the exact spot where the attempt happened. Check it out. Here is the Wikipedia article on the Reagan assassination attempt, and below is the image I captured. The Wiki article is worth revisiting to refresh your memory, if for nothing else. For example, I forgot that used explosive bullets in his attempt.
And today? Nothing. There’s no plaque, no sign, no footnote to history that anything remarkable ever happened here. Sure, there’s a bit shrubbery now that wasn’t there at the time of the event… but that’s about the only visible change since that fateful day.