The mid-term electorate this year will be as white as America was in 1983, and as old as it will be in 2050

WHAT bliss it was to be alive. Ronald Reagan was ignoring the budget deficit, the Marines were booting Communists out of Grenada and the Chicken McNugget was first clasped between the thumb and forefinger of a delighted nation. As November’s mid-term elections approach, and with them the possibility of the Senate flipping from Democratic to Republican control, keep 1983 in mind.

America that year was 77% white, a proportion that has since declined rapidly as a result of births to non-whites and immigration (see chart). That number, 77%, is also the share of votes cast by whites in 2010, the most recent mid-term election. Racially, mid-term voters lag the changes in the voting-age population by about 20 years and the country as a whole by nearly 30.

Demography does not translate neatly into politics. Both Henry Waxman, a veteran liberal from California, and Eric Cantor, a Virginia congressman who until recently was a conservative pin-up, hail from districts that are miniature versions of the mid-term electorate. But of the 30-odd districts that cluster around the 77%-white mark, most are held by Republicans.

If November’s voters are, in racial terms, America’s past then they also offer a glimpse of its future. Mid-term voters are disproportionately old: a quarter of those who told the Census Bureau that they voted in 2010 were over 65, though only 13% of Americans have that distinction. In terms of age, the country as a whole will not catch up with today’s voters until after 2050, according to projections from the Census Bureau. At that point, 21% of Americans will be over 65.

Congressional districts with such high proportions of old voters are rare. Only 11 of the 435 members of the House represent districts where more than a fifth of residents are over 65: one is in Arizona, the rest are in Florida. Only three of them have Democratic congressmen—all Florida districts filled with retired New Yorkers who bring their politics with them. The age of the mid-term electorate helps to explain why even ardent fiscal conservatives avoid talking about cuts to Medicare or Social Security on the campaign trail.

Taken together, race and age help to explain why the Democrats face such a struggle in November. The party does comparatively badly with older, whiter voters, a vulnerability that is exposed in mid-term elections because of low turnout.

When the presidency is up for grabs, many more Americans bother to vote. In mid-term elections, apathy reigns: 35m fewer people voted in 2010 than in 2012. Only the most committed make it to a polling booth, and they are disproportionately frail and pale. In other words, the America that votes in mid-terms is quite unlike the America that breathes.

This need not doom Democrats. The party has gained plenty of seats in previous mid-term elections. What makes things truly difficult for Democrats is the addition of a third handicap: that one of their number is president. For all the contempt that voters have for malfunctioning Washington, they rather like divided government. The party that holds the White House has lost seats in all but three of the past 19 mid-terms. This gives the other party an incentive to be as obstructive as possible, in the hope that the next Congress will include more of its members (a tactic Democrats honed when George W. Bush was in office and Republicans have perfected now that Barack Obama is).

For any sitting Democrat, however, the handicap of belonging to the president’s party must be weighed against the advantages of incumbency. Any incumbent congressman or senator has a big head start: greater name-recognition, more money to campaign with, the ability to shovel federal dollars into local pockets and so forth. While Americans are contemptuous of politicians as a group, they are often fond of their own representatives. John Sides of George Washington University has crunched data on Senate elections since 1980 and determined that incumbency is worth 2.4 percentage points of the vote at a mid-term election, nearly making up for the three-point penalty for having your guy in the White House, other things being equal (which they rarely are).

What does this mean for the Republicans’ chances of winning the six seats they need to capture the Senate? Seven Democratic senators represent states that Mitt Romney won in 2012. Two of those are open elections, meaning the incumbent is not standing. These seats, in West Virginia (see Lexington) and South Dakota, are likely to turn red, as is Montana, where the sitting Democrat was appointed as a replacement for Max Baucus, now America’s ambassador to China.

That leaves Republicans needing three seats from the remaining four states won by Mr Romney: Alaska, Arkansas, Louisiana and North Carolina. If the GOP fails to win two of that quartet, it might pick up seats in Iowa and Michigan instead, states that Mr Obama won but where there is no incumbent running.

The success of Nate Silver, then the New York Times’s prognosticator, in calling every state correctly before the 2012 presidential election has drawn more people into the game of predicting election results. This is harder to do for Senate elections than for a presidential vote because there are less good data to go on (state polls are less frequent and often rely on small samples), because there are more candidates to evaluate and because the attachment of a state to its senator can be hard to quantify.

With that caveat, the consensus among forecasters is currently that the Republicans are slightly more likely to take the Senate than the Democrats are to hold it, but that the probability of either outcome is currently not so different from the chance of a flipped coin coming up heads.

If that portends a frustrating end to Mr Obama’s second term, in which the president’s power is limited to executive actions and vetoes, Democrats should not be too downcast. If they do lose the Senate they will have a good chance of taking it back in 2016, when the map of states being contested will be more favourable to their party and the colouring of the electorate may even have entered the 1990s.