Quite likely, I’m afraid. Most likely by a terrorist group acting as proxy for a rogue state. Likely to be smuggled to the target rather than launched or dropped. Ship or cargo aicraft with a suicide crew. Nuclear devices have a characteristic “fingerprint” of isotopes upon detonation that would lead back to state of origin, so retribution would be the order of the day.
New York or San Francisco would be traded for Teheran or Pyonyang. A nuclear device used against the US would provoke a knee-jerk automatic counterstrike within days. Any political figure opposing such would be shouted down and career over, like Jeanette Rankin after Pearl Harbor or Patricia Schroeder after 9/11.