Every year in June, on a warm and sticky Thursday, senators arrive at work looking like they’ve come straight from the Kentucky Derby. Gone are the standard dark suits of the winter months. Instead, they wear seersucker.

Walking the halls of the Capitol, they project a sense of gentility and ease. Why yes, they seem to say, this fabric is 100 percent cotton. Why yes, it is extremely cool. Why yes, these tiny stripes, blue and white and vanishingly thin, kind of make your head spin. Now let’s all squeeze together for a bipartisan photo op.