Whatever your opinion of President Obama, there's no question he has spectacularly revived the number and quality of musical performances in the White House. Look no further than "Paul McCartney: The Library of Congress Gershwin Prize for Popular Song in Performance at the White House," taped early last month and screening on PBS on Wednesday, the fourth "In Performance" show thus far during his young administration. Yes, Sir Paul is English. But the award is not restricted to U.S. citizens. Named in honor of brothers Ira and George Gershwin, the award is given to a composer or performer whose lifetime...