The cobalt-salted bombs weren’t Teller’s idea. That came from Leo Szilard. He intended his ideas as a warning, not for military application. As one might have expected, the lunatic LeMay wanted to run with it and was (I guess) eventually shut down.
During the Korean War, North Korea had not committed any offense comparable to nuking DC, yet we waged a campaign of strategic bombing that reduced the country to rubble and killed an estimated two million people, almost entirely civilians, according to statistician Matthew White, self-described “atrocitologist.” One American colonel who was captured and transported north said it looked like the surface of the moon, and he saw no intact buildings.
I do not pretend to predict our reaction to our capital being nuked, but I have no confidence it would be proportionate or morally examined.