Political prognostication is a fool’s game and arguably a distraction from the important work of citizens, which is to influence–not to forecast–the future.
But I can’t resist.
Recent projections give the Democrats anywhere from a 39% to a 58% (or even 63%) chance of winning the House. One reputable model gives the Democrats a 30% chance of winning the Senate. Those two results are not truly independent, since both will be affected by the national situation in November. But they are substantially independent, as illustrated by the claim that an 8 percentage-point swing toward the Democrats would give them 44 more House seats and four fewer Senate seats. If we assume that the two elections are independent events, then Democrats have between a 43% and 70% chance of capturing at least one house of Congress.
The wildcard is how the national situation will change between now and late October. If there’s a terrorist attack on the US, it will probably help the president’s party. The nomination battle could boost Republicans by giving religious conservatives a reason to turn out and by putting red-state Democratic Senators in a tough spot. Another four months of economic growth might help the GOP a bit, as would a report from the Special Counsel that comes nowhere close to associating Trump with crimes.
But I think upcoming news is more likely to assist the Democrats. Trump and his party have already captured whatever political benefit they’re going to gain from the economy, and there’s a significant potential for economic turbulence ahead. The Mueller investigation has lost public support without yielding a damaging public report, but his report is coming. Since 67% of Americans want to preserve Roe v Wade, a nomination that places that decision in jeopardy could mobilize more people against Trump than for him. The North Korea summit was a political success for the president: he hyped a genuine crisis to the maximum and then declared it resolved, which convinced a bunch of Americans. But that domestic political gain is fragile, since the threat was not actually resolved. We can also expect massive Obamacare premium increases, ugly battles in Congress, plenty of awkward votes for Republican incumbents, a possibly damaging Special Counsel report, lawsuits and depositions against the president, and unpredictable controversies revolving around him.
Overall, I’d put the chances that the Democrats control at least one house of Congress above 70%. That estimate is compatible with any actual result in November, so there’s no way I can be proven wrong. Meanwhile, stop reading forecasts and get back to work!