Biden's latest stumble comes days after some questioned why a "watch your step" sign was spotted on the stairs leading up to Air Force One during Biden's arrival in the U.K. on Sunday night.

Watch Your Step! By Lori Yerdon, U.S. Army Combat Readiness/Safety Center, Fort Rucker, Ala. March 28, 2012 Share on Twitter; Share on Facebook; Share on Reddit; Share on LinkedIn ...