Hillary Clinton now has only a tiny lead in the polls over Donald Trump, but she can still profit from a favorable electoral college map, notably because of her competitiveness in swing states like Ohio, Virginia, North Carolina and Florida (Trump should win in all of them to be elected). However, even if she prevailed on November 8, a President Clinton in a Congress controlled by Republicans would possibly accomplish nothing. The US president may be the leader of the only superpower on earth, but he or she must negotiate every trivial move (except bombing Syria or Yemen) with unruly senators and representatives, the majority of whom are now Republicans.
Therefore, at this point in the campaign, the Big Question is: “Will Democrats transform a presidential victory in new majorities in the Senate and the House, too?” The GOP now holds 54 of the 100 seats in the Senate and 246 of the 435 seats in the House, a majority in both chambers. The answer will depend on places like the 2nd district of Arizona (home of Bob Birch, one of the main characters of House of Cards). In the real world, the district covers two-thirds of the city of Tucson and its representative, Republican Martha McSally, edged her opponent by only 161 votes in 2014, after losing to him by 2,500 in 2012.
These are the swing districts, that can change hands at every election. However, there are very few of them. One of the peculiar consequences of US federalism is that states can draw the borders of the 435 single-seat constituencies almost at will. Partisan legislatures use and abuse this power after each census. As a result, popular vote and number of seats obtained by a party do not align very well.
After 2010, gerrymandering has been pushed to the extreme by Republicans, who take advantage of their control of a majority of state legislatures. The consequence is that they now have an almost election-proof majority, because districts are designed in such a way that incumbents always win, at least in normal political circumstances. The respected Cook Political Report considers only 19 seats as “toss-ups” in November, meaning those where the result is really unpredictable. Nineteen seats to which we can add 18 more seats that lean to one side or the other but could still create the surprise. That makes a grand total of 37 seats, precisely 8,5% of the House, meaning that in this democratic institution 91.5% of the constituencies are somehow “reserved” for one party or the other.
McSally’s Arizona seat is vulnerable to a surge of Democratic voters, mobilized against Trump; it remains to be seen what can happens in other districts like California-21 (San Joaquin Valley) where Republican David Valadao obtained 12,500 more votes than his opponent in 2014 but 71% of the population is Hispanic. If we look at New Jersey-5, where Republican Scott Garrett had an advantage of 23,000 votes over his Democratic competitor, we realize that the district became more favorable to the Democrats in recent years and therefore the 2016 election may be uncertain.
To win the majority in the House (218 seats), Democrats need to keep all their incumbents in place and prevail in 30 more races, which means to win all the competitive districts, and at least four of the eleven districts that so far are still considered favorable to the Republican candidates. Is it possible? Yes, if Republican voters who despise Trump choose not to show up at the polls in November. No, if Republican supporters and Independents turn out in large numbers, motivated by hatred of Clinton and emotion created by terrorist acts.
If Hillary wins with a margin at least as large as Barack Obama’s in 2008 (53% to 47%), dislodging the entrenched Republican majority in the House appears to be a daunting task for the Democrats. Presidential years are more favorable to them, but in 2012 their candidates in the House collected 1.6 million votes more than the Republicans, 50.7% of the popular vote, and won only 201 seats, against 234 for the GOP.
A reason for optimism comes from the fact that in recent years American voters tend to choose a straight ticket, voting for all the candidates of the same party, from president to senator, representative, and governor – the Supreme Court forbade Minnesota from suppressing this possibility in the coming elections. Since 1992, elections have become much more national and polarized: Democratic candidates 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 in the House. Republicans won in 2000 and 2004, and the House went in the same direction both times.
This means that an unpopular candidate like Trump at the top of the ticket is a handicap for all the other Republicans down ballot. How much this disadvantage will translate into votes for Democratic candidates in the House remains to be seen.