Talk about the perfect confluence of liberal politics and show biz: Paul McCartney serenading first lady Michelle Obama in the East Room of the White House this week. Sir Paul, 67, came to pick up his Gershwin Prize for Popular Song and couldn’t resist some “Michelle, my belle,” just for Mrs. Obama. It wouldn’t have been the aforementioned nexus of pop and political glitz without a gratuitous jab at former President Bush. Thanking the award sponsor (Library of Congress), McCartney got off this riff: “After the last eight years, it’s good to have a president that knows what a library is.” Hahahahahahahahahahahah! Now that’s a good one — just the kind of yuk liberals entertain themselves with at the expense of someone who got his bachelor’s at Yale, his MBA at Harvard Business School and who married a librarian.