The 1890 Busch Building in the photo was acquired by Lansburgh's in 1921 and amalgamated with adjacent buildings as part of their big flagship department store. Now Lansburgh's is long gone and the building is part of the Penn Quarter revitalization.
http://www.thedepartmentstoremuseum.org/2010/06/lansburgh-brother-washin...

The only building remaining that I can see is the tall building halfway down the block. They have replaced the flagpole with two additional stories, but it has the same ornamentation.

The southeast corner of the intersection (at far left) was, and still is, occupied by a Civil War-era three story building where Clara Barton of Red Cross fame established her "Missing Soldiers Office" in 1865. Through 1868, the Missing Soldiers Office 'had received 63,182 inquiries, written 41,855 letters, mailed 58,693 printed circulars, distributed 99,057 copies of her printed rolls, and identified 22,000 men.” The Office was lost to history, then rediscovered around 1996. Restored, the third floor is now a public museum.
https://clarabartonmuseum.org/

The tallest building in the 1901 photo, the Busch building, with a current address of 750 E Street NW, is still standing. What is now on the corner has come up to its height.

Right on the corner, one of the ubiquitous DC call box frames for fire and police--though curiously missing its innards (the actual call box). These were installed starting in 1873; when I moved to the area in the early 1980s, they had just been phased out, though many still had a working light at the top of the frame.

Though not quite ubiquitous, the frames are still much in evidence around the city. There have been various formal and informal projects to turn them into information points or street artworks.