As Hillary Clinton’s road to 270 electoral votes has turned rockier, Democrats have begun to encourage each other with a different number: you can almost hear the chant: “two-forty-two! two-forty-two.” That’s the total vote of the nineteen states (and Washington D.C.) that have gone Democrat in every one of the last six elections. It’s their firewall, they insist, putting Clinton in a position to pick up the remaining twenty-eight electoral votes in all sorts of ways.

“Florida alone will do it!… Or Virginia and North Carolina! Or..”

The arithmetic may be right, but the underlying assumption isn’t. Indeed, the whole idea of an “electoral lock” all but ensuring a Democratic victory can be accurately judged by the not-so-distant past; when it was in very different hands.

After 1988, the Republican Party had won five of six Presidential elections. Their only loss was a very narrow defeat, when Gerald Ford won 240 electoral votes to Jimmy Carter’s 298. (A shift of 5,500 votes in Ohio and 7,000 votes in Mississippi would have given Ford another term, just as a shift of a few hundred votes in Florida in 2000 would have put Al Gore in the White House.) That GOP lock was formidable: most of New England, just about all of the South (except when Southerner Carter ran in 1976), the plains states and the interior West.

Perhaps most remarkably, the Republicans held what seemed to be an iron grip on three big states: New Jersey, Illinois and California had gone Republican six straight times. (In fact, California had voted Democratic only once from 1952 to 1988).

What happened? States are not walled off from each other: when the country chose a Democratic President in 1992 by a five million vote margin, millions of voters in those states shifted their preference. The big electoral prizes of California, Illinois and New Jersey all went for Clinton, and they have not been remotely competitive since. ...