The Warren G Harding Home...now the Monaco embassy. It's located at 1612 21st Street, NW. In July 1917, the Hardings purchased this house, a neo-Georgian style duplex with a terrace and a side entrance. They lived in this house through the end of his Senate term, though Harding used his home in Marion, Ohio during the summer of 1920 to conduct his famous “front porch” campaign. In November 1920, Harding defeated Democrat James M. Cox of Ohio for the Presidency. He resigned from the Senate in December 1920 and was inaugurated as the 29th President on March 4, 1921. This home is now privately owned - and it occupied by the Embassy of Monaco.
   This is a free attraction from the outside but I don't know about going inside.  It's possible it's a residence to the Monaco Ambassador in addition.  If not, you may be able to ask to see it. But it's not a "tourist" attraction.