HMS Warrior against USS Monitor

Could American guns or ironclads threaten HMS Warrior in an 1860s Anglo-American war?

Only under restrictive coastal conditions; in an open-sea fight Warrior's speed, maneuver, and power made her overwhelmingly favored.

American guns might damage Warrior, but the ship-to-ship matchup depended heavily on setting. In open water Warrior's speed and maneuver made Monitor extremely vulnerable, potentially even to ramming; only a restricted close-shore fight gave the monitor a narrow opportunity. The United States possessed weapons that could threaten the British ironclad, but lacked a comparable seagoing ship able to impose favorable conditions. This makes geography and mobility more decisive than a simple armor-and-gun comparison.