America has just exited a biennium of Democratic trifecta -- control by the nation’s and the world’s oldest political party of the White House and majorities in the Senate and House of Representatives. It is only the third such biennium in the last 40 years, since 1993-95 and 2009-11, the first two years of the Clinton and Obama administrations. It was a rare opportunity, then, for the party in…