Mon Sep 23

Harris’ post-debate gains sustained in US polls, but Republicans likely to gain Senate control

Written by: Adrian Beaumont, Election Analyst (Psephologist) at The Conversation; and Honorary Associate, School of Mathematics and Statistics, The University of Melbourne

The United States presidential election will be held on November 5. In analyst Nate Silver’s aggregate ^[1] of national polls, Democrat Kamala Harris leads Republican Donald Trump by 49.2–46.2. In my previous US politics article ^[2] last Wednesday, Harris led Trump by 48.9–46.0.

Joe Biden’s final position before his withdrawal as Democratic candidate on July 21 was a national poll deficit against Trump of 45.2–41.2.

It’s been nearly two weeks since the September 10 debate between Harris and Trump. In my previous article I was sceptical that Harris’ post-debate gains would be sustained, but they have been.

The US president isn’t elected by the national popular vote, but by the Electoral College, in which each state receives electoral votes equal to its federal House seats (population based) and senators (always two). Almost all states award their electoral votes as winner takes all, and it takes 270 electoral votes to win (out of 538 total).

The Electoral College is biased to Trump relative to the national popular vote, with Harris needing at least a two-point popular vote win in Silver’s model to be the Electoral College favourite.

Harris’ Electoral College win probability fell to a low of 35% on September 9 in Silver’s model, but she has surged back to favouritism with a 54% win probability, up from 43.5% last Wednesday. Silver’s model is now in better agreement with the FiveThirtyEight model ^[3], which gives Harris a 62% win probability.

Pennsylvania is the most important swing state with 19 electoral votes, and Harris now leads there by 1.5 points, gaining 1.4 points since last week. Harris also has narrow leads in Michigan, Wisconsin and Nevada. If Harris wins all states she currently leads in, she wins the Electoral College ^[4] by 276–262.

Since my previous US article on Wednesday, Harris has continued to get good national polls and better polls from Pennsylvania and Michigan (15 electoral votes). This explains why she is again the favourite in Silver’s model after Trump had been the favourite from late August until last Thursday.

In North Carolina, Trump leads by just 0.1 point, but there’s been a scandal ^[5] about Republican gubernatorial candidate Mark Robinson that broke Thursday, and there haven’t yet been North Carolina polls taken since this scandal. This scandal may hurt Trump in North Carolina, which has 16 electoral votes.

Favourability ratings and economic news

Harris now has a barely positive net favourability in the national FiveThirtyEight aggregate ^[6], at +0.3, with 46.9% favourable and 46.6% unfavourable. After large early gains, her ratings have improved slowly in the last month. Trump’s net favourability is -10.1, with 52.8% unfavourable and 42.7% favourable; his ratings are barely changed in the last month.

Trump’s running mate JD Vance is unpopular with a -10.8 net favourable rating, while Harris’ running mate Tim Walz has a +3.8 net favourable, making him the most popular of the four. Biden remains unpopular with a -15.3 net approval. It’s best for Harris if Biden stays out of the headlines.

In economic news, the US Federal Reserve cut interest rates ^[7] by 0.5 points last Wednesday, the first time they have been reduced since 2020. Rates had risen from nearly zero to over 5% from 2022 to 2023.

Silver’s economic index that averages six indicators is currently at +0.10. Many on the left despise the stock market, but its recent performance is offsetting worse data in other indicators.

Republicans likely to gain Senate control

Elections for the House of Representatives and Senate will be held concurrently with the presidential election on November 5. Single-member districts are used to elect the 435 House members, with states apportioned House seats on a population basis.

House terms are only two years, so the last election of the House ^[8] was at the November 2022 midterm elections, when Republicans won the House by 222 seats to 213 for Democrats on a national popular vote share of 50.0–47.3.

The FiveThirtyEight aggregate ^[9] of polls of the national House popular vote has Democrats ahead by 46.7–44.5. If Harris wins, Democrats have a good chance to regain control of the House.

There are two senators for each of the 50 states. Senators have six-year terms, with one-third up for election every two years. Including independents who caucus with them, Democrats currently control ^[10] the 100-member Senate by a 51–49 margin.

This year Democrats and aligned independents will be defending 23 of the 33 regular Senate seats up for election (there will also be a byelection in the safely Republican Nebraska). Trump won West Virginia, Montana and Ohio easily in both 2016 and 2020, and Democrats are defending seats in all three states.

With the retirement of former Democratic Senator (now independent) Joe Manchin, West Virginia is certain to be a Republican gain at this election, and the Republicans are also well ahead in Montana ^[11]. If no other seats change hands, gaining West Virginia and Montana will give Republicans a 51–49 Senate majority.

Democrats are just ahead in Ohio and have larger leads in Senate races in the presidential swing states of Arizona, Wisconsin, Nevada, Michigan and Pennsylvania (all Democratic held). They have outside chances of gaining seats in Florida and Texas.

Even if Harris wins, Republicans are likely to gain at least a 51–49 Senate majority. The two senators per state rule advantages Republicans as they dominate low-population, rural states.

If Democrats lose the Senate, even if Harris wins the presidency, Republicans would have a veto over Harris’ legislation, and her cabinet and judicial appointments. That means no left-wing judge would be appointed to the Supreme Court if a vacancy occurred.