It’s always possible that events — such as a recession — would temper some of these ambitions. Republicans also feared the worst in 1993 when Democrats ran the entire government, but it didn’t turn out that way. On the other hand, Bob Dole then had 43 GOP Senators to support a filibuster, and the entire Democratic Party has since moved sharply to the left. Mr. Obama’s agenda is far more liberal than Bill Clinton’s was in 1992, and the Southern Democrats who killed Al Gore’s BTU tax and modified liberal ambitions are long gone.

In both 1933 and 1965, liberal majorities imposed vast expansions of government that have never been repealed, and the current financial panic may give today’s left another pretext to return to those heydays of welfare-state liberalism. Americans voting for “change” should know they may get far more than they ever imagined.