A mighty sigh - equal parts frustration and resignation - seems to animate 'Hillary and Clinton,' Lucas Hnath's piquant, slender new play about ... well, it's about exactly what, and whom, its title suggests. This production, which opened on Thursday night at the Golden Theater under the suave direction of Joe Mantello, is indeed a portrait of a marriage between two extremely well-known American politicians. As for that propulsive sigh, it emanates from the title character called Hillary, who spends the surprisingly airy 90 minutes of this show in what might be called a state of angry wistfulness. It is our very good fortune that Hillary is portrayed by Laurie Metcalf, an actress who does being thwarted better than anyone.