Can the Democrats take control of Congress in November?

The Democrats are optimistic. Looking at Hillary Clinton’s steady lead in the polls over Donald Trump, they are feeling confident of winning the White House in November. The US president is not directly elected—instead, votes are consolidated in each state, something that modifies or even subverts the popular vote (as happened in 2000, when Al Gore received 543,895 more votes than George W Bush but still lost). In 2016, this mechanism is supposed to favour Clinton because of her strength in swing states like Ohio, Virginia, Pennsylvania, North Carolina and Florida.

So, the question is: “Will Democrats transform a presidential success into new majorities in the Senate and the House?” This is by no means a curiosity: a President Clinton in a Congress  controlled by Republicans will accomplish nothing. Far from being the most powerful individual in the world, the American president must negotiate every trivial move (except, as commander-in-chief, bombing Syria or Yemen) with often rebellious senators and representatives.

The GOP currently holds a majority in both chambers of the US legislature, the Senate and the House of Representatives. The Democrats’ optimism comes from the fact that in recent years American voters have tended to choose a straight ticket, voting for all the candidates of the same party, from President to Senator, Representative, Governor and even school superintendent or dog-catcher. And the Democrats do have a chance of taking the Senate, as more Republicans than Democrats are among the 34 senators up for re-election in November.

But straight-ticket voting is a phenomenon of the last 20 years. Democrats controlled the House of Representatives for 46 years between 1949 and 1995, while Republicans occupied the White House with Dwight Eisenhower, Richard Nixon, Gerald Ford, Ronald Reagan and George H W Bush. For example, in 1980, Ronald Reagan obtained 43.9m votes, crushing Democrat Jimmy Carter, but Republican candidates in the House gathered only 37m ballots. People were attached to “their” representative and voted to re-elect him or her, no matter whom they chose as President.

Since 1992, elections became much more polarized. Democrats Bill Clinton and Barack Obama won the presidency in 1992, 1996, 2008 and 2012 and in every one of these elections, the party also collected a majority of the popular vote for the House. Republican George W Bush won the presidency in 2000 and 2004, and the House went in the same direction both times.

Like the UK, the US Congress is made of single-seat constituencies, where the first-past-the-post candidate wins. The important difference with the UK, however, is that American states can redraw the borders of House constituencies almost at will and partisan legislatures use and abuse this power after each census. (This does not apply to the Senate, which uses the fixed state borders.) Redistricting has more or less turned into gerrymandering, with sophisticated demographic and socioeconomical analysis used to pack likely voters of one party into a few districts, leaving room for candidates of the other party to sail to victory in other districts. As a result, the popular vote and number of seats obtained by a party in the House do not align very well.

In the UK, historians remind us of the general election of 1951, when the Tories obtained 321 seats, 26 more than Labour, even though they lost the popular vote by 231,000. But that was a rare event; in the US, it is now common. In 2012, Democrats collected 1.6m votes more than Republicans, 50.7 per cent of the popular vote, but won only 201 seats, against 234 for the GOP. Gerrymandering has been pushed to the extreme by Republicans since 2010, when they gained a majority of state legislatures. They now have an almost election-proof majority in the House, because districts are designed so that only a small number of them can change hands in normal circumstances. Cook Political Reports estimates that in November, only 19 seats are “toss-up”: those where the result is really unpredictable. Eighteen more seats lean to one side or the other but could still create upsets. That makes a grand total of 37 seats, or 8.5 per cent of the House. In this democratic body, 91.5 per cent of the constituencies are somehow reserved for one party or the other.

All 435 seats in the House will be up for re-election in November. To win a majority (218 seats), Democrats need to keep in place all their incumbents and prevail in 30 more races, which means to win all the “toss-up” districts and four of the 11 districts that are still considered favorable for the Republican candidates. Is it possible? Yes, if those Republican voters who do not like Trump sit on their hands and do not go to the polls in November. But all those same voters could go to the polls and cast their vote for a third-party candidate, or even for Hillary but remain faithful to their senator or representative. In any event, a Democratic majority in the House after the 8th November remains still a long shot.