Driving on I-79 south from Pittsburgh toward Charlottesville, I started composing this birthday card in my head—a love letter to America on its 250th birthday. The hills of Pennsylvania were blanketed in glittering white snow from which bare-armed trees rose like the locals: lean, weathered, lined and stained like the earth. In a frozen sales lot beside the road, 50 John Deere tractors stood in formation, their booms raised toward the sky like eaglets waiting to be fed. At the crest of one…