The star-studded In Performance at the White House: Red, White & Blues special that was taped last Tuesday airs tonight at 9 on WHYY and other PBS stations. As was widely reported last week, Barack Obama joined in at the end on an all-hands-on-deck version of "Sweet Home Chicago," along with B.B. King, Buddy Guy, Mick Jagger, Shemekia Copeland, Jeff Beck, Gary Clark Jr., Trombone Shorty, and a whole bunch of other. Here's a clip of POTUS putting on his rock-critic hat and eloquently talking about the fateful meeting between folklorist Alan Lomax and McKinley Morganfield, a.k.a. Muddy Waters, on Stovall's Plantation in Mississippi in 1941, before he introduced King to the White House crowd.