That Hubert H. Humphrey building is sure ugly. But it was built in the 1970s. The FBI Headquarters building in Wash DC hails from the same style and era. The late 1960s World Trade Center towers are the same style.
But would you call block architecture from the 1960s/70s modern?
I would call the older buildings, from the 19th century through the 1910s CLASSIC, and the 1920s through 1930s Art Deco. The more modern look came from WWII hurry-up building program in Washington, such as the Pentagon.
We should go back to classical. Roman, Creek Revival, Colonial, Baroque, they’re all beautiful in their way.
1970s building are “Brutalist”. I actually like it. DC Metro is the best example of that architecture.