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.

Now look at the states where Democrats allegedly now hold the key. In some of them, Democrats have barely prevailed; Gore won Wisconsin in 2000 by two-tenths of one per cent; he won Oregon by half of one per cent. In 2004, John Kerry took Wisconsin by half of one per cent; and Pennsylvania was a two-and-a-half point win.

Even when you look at President Obama’s two victories, where he won those “electoral lock” states by comfortable pluralities, the picture is less than reassuring. Had he lost Florida and Ohio, his 332 electoral vote total would have shrunk to 285. The polls now show both of those states within Donald Trump’s reach; add to that Clinton’s troubles in Iowa, Nevada, New Hampshire, and North Carolina and it’s not hard to see how she could lose even if she holds on to those 242 electoral votes.

Yes, there may be an opportunity to expand the map in a place like Georgia, but there’s also a chance that the state most coveted by Republicans could be in play. For two decades, Pennsylvania has been to the GOP what Lucy and her football has been to Charlie Brown. But should Trump actually find those elusive missing white voters between Philadelphia and Pittsburgh, a keystone of the Democrats’ electoral lock assumption crumbles.

One footnote: there are times when states change their political colors dramatically and, in political terms, fairly quickly. West Virginia was as Democratic a redoubt as possible in the last decades of the last century. It was one of only six states that went with Jimmy Carter in 1980; one of only 10 that went with Michael Dukakis in 1988. But it chose George W. Bush over Al Gore in 2000, and now it is bright red. (Yes, race may well have mattered in Obama’s 27-point loss there, but it went with Bush over Kerry in 2004 by 13 points. By contrast, Connecticut, which chose Nixon, Ford, Reagan and George W. Bush, is now firmly part of the Democratic base.

So what does this race come down to? Yes, states and their electors decide who is President. But if Clinton winds up losing the popular vote by more than a point or two, those deep-blue states will not save her. Some of them may not be blue at all.