Wearing white cowboy hat, black suit and black tie, country singer and guitar virtuoso Brad Paisley strode on stage in the East Room of the White House before a bipartisan audience. It was a Saturday night and, fittingly, he began the 40-minute set playing his hit song American Saturday Night – but with an amended lyric. “I had to change the second line because it mentioned Russia, and I don’t do that any more,” he explained. When Paisley delivered its substitute – “There’s a Ukrainian flag hanging up behind the bar” – no one applauded louder than Joe Biden in...