The race for the United States Senate

Democrats are narrow favourites in the battle for the United States Senate – control of which will be critical if Biden is to implement his agenda.

The untimely death of progressive Supreme Court justice Ruth Bader Ginsburg has brought into focus the power of the United States Senate and how critical it has been for Republicans to maintain conservative control of the powerful court.

In my last two posts, I previewed the United States presidential election where Joe Biden is the favourite to beat Donald Trump. But for Biden to achieve any of the reforms he has committed to implementing, he will also need Democrats to gain control of Congress. Congress is made up of the House of Representatives and the Senate. 

Democrats took control of the House of Representatives in 2018 and they should have comparatively little difficulty holding it in 2020. The Senate, however, is a different matter. This blog post will preview the 2020 Senate election.


Compared to the electoral college (the system used to elect a president), the Senate is simple. There are 100 seats, with each of the 50 states electing two senators. Around one third of senators are up for election every two years with each senator serving a six-year term. Winning a Senate seat requires winning a statewide vote. Usually just one senator in each state faces election at the same time (eg. one senator from Michigan faced an election in 2018 and the second senator faces election this year). With 33-34 senators up for election at any one time, this means not every state will have a senate election every two years.

This means that a strong performance nationally does not always translate into gains in the Senate. This can cause some seemingly counter-intuitive impacts on the make-up of the Senate.

Here are some examples. In 2018, Democrats had a massive win in the popular vote, beating Republicans in the House of Representatives by 9 points. Yet Democrats actually lost Senate seats that year (going from 49 to 47). 

And in 2016, Republicans narrowly won a swath of Senate seats in Pennsylvania, Wisconsin and Florida. Democrats trounced Republicans in Pennsylvania and Wisconsin in 2018 and may do so again in 2020 – but this will not win them any Senate seats because 2016 senators will not face election until 2022!

Because of these idiosyncrasies, Republicans are on the defensive in many Senate seats this year but it will take a very strong performance from Democrats to gain control. Biden may win the popular vote for president by 5-8 points but Democrats may only be able to eke out a Senate majority of just one or two seats. A smaller Biden win could leave the Senate in the hands of Republicans. 

Going in to 2020, the Republicans have a narrow majority: 53 seats to Democrats’ 47.

There are a couple of seats this year that Republicans could gain and a much larger number of seats that Democrats are targeting. Let’s look at each of these groups in turn.

Rather than using a polling average like I did for my previous post on the presidential election, today I will use FiveThirtyEight’s Senate forecast, which incorporates polling averages and a range of other inputs to forecast likely results. I will include all states where either party has a greater than 10% chance of winning a Senate seat off the other party.

Please note that the numbers below are probabilities that a party will win a seat, not a projection of the winning margin (eg. Republicans have a 77% of winning Alabama. They will not win the vote in Alabama by 77%).

Potential Republican gains

  • Alabama – Republicans have a 77% chance of winning
  • Michigan – Republicans have a 22% chance of winning

There are very few pick-up opportunities for Republicans this year: senators facing election in 2020 were first elected in 2014, the year Republicans swept many competitive Senate seats and took control of the Senate from Democrats, who had held a Senate majority from 2006 to 2014.

Republicans are favourites to win Alabama. Alabama is one of the most strongly Republican and pro-Trump states in the country so it will be difficult for Democratic Senator Doug Jones to hold on to this seat. 

You may be thinking, how did Democrats win this seat in the first place? Well, a special election (similar to a by-election in Australian terminology) was held in 2017 to fill this vacant seat and Republicans selected a candidate who faced accusations of child sexual abuse. Not great for winning elections, huh? Alabama may be one of the most pro-Republican states in the country but when faced with the choice of a Republican accused of abusing children and a Democrat not accused of abusing children, it is hardly surprising that voters chose the latter. 

This year, Doug Jones will face a far less problematic Republican candidate and Republicans are favoured to win back the seat.

The only other serious pick-up opportunity for Republicans is in Michigan but with Joe Biden holding a large lead there in the presidential race, this seems unlikely. But if Trump does much better than expected, it is certainly possible for Republicans to win this seat.

Potential Democratic gains

  • Arizona – Democrats have a 77% chance of winning
  • Colorado – Democrats have a 71% chance of winning
  • North Carolina – Democrats have a 63% chance of winning
  • Maine – Democrats have a 59% chance of winning
  • Iowa – Democrats have a 47% chance of winning
  • Montana – Democrats have a 34% chance of winning
  • Georgia – Democrats have a 26% chance of winning
  • Kansas – Democrats have a 20% chance of winning
  • Georgia special election – Democrats have a 19% chance of winning
  • South Carolina – Democrats have a 18% chance of winning
  • Alaska – Democrats have a 14% chance of winning
  • Texas – Democrats have a 13% chance of winning

As you can see, there are way more potential gains for Democrats this year than Republicans. Democrats are currently favoured to win three Senate seats off Republicans, with another two seats too close to call. Democrats are also competitive in another seven seats.

The most likely pick-ups for Democrats are in Arizona and Colorado. Colorado is polling very strongly for Biden and he has consistently led in Arizona (albeit by a much smaller margin). Despite their clear vulnerabilities, the incumbent Republican senators in these states have strongly backed Trump at every turn, making their re-election that much harder. Democrats would be feeling very confident of picking up these two seats.

Democrats would also be feeling confident about North Carolina. Biden is only narrowly ahead there in the presidential race but the incumbent Republican senator has been polling pretty poorly. It’s still a bit early, but things are looking good for Democrats here.

Maine and Iowa loom as crucial states that will go a long way to determining which party controls the Senate. 

Democrats are currently polling well in Maine but there a number of factors that make this race more uncertain. A lot of this comes down to the long-serving incumbent Republican Senator Susan Collins. She has been a bit of a maverick in Maine and historically has had no difficulty winning by huge margins despite Maine being a generally Democratic leaning-state. She has also voted against Trump’s policies more than any other Republican senator. Will Collins be able to maintain support from moderate Democratic voters who have crossed party lines to vote for her in previous elections? The polling suggests not but the race may be close.

Iowa is currently the most competitive Senate race. The FiveThirtyEight forecast shows the race as a virtual tie, although the Democratic candidate has been pulling ahead in recent polls. This race could go either way but this seat will be critical for Democrats to reach 51 seats if they lose Alabama to Republicans. 

Beyond Iowa, there are seven other states where FiveThirtyEight currently gives Democrats a greater than 10% chance of winning. The most likely of these are Montana, Kansas, the two Georgia seats and South Carolina, where Republicans lead by very narrow margins in polls. Alaska and Texas are also possible gains but probably out of reach unless the Democratic candidates do better than the polls currently indicate.

Summing up

If we assume Republicans win Alabama and Democrats win Arizona, Colorado, North Carolina and Maine, this would result in a Senate split between each party of exactly 50-50.

If the Senate is deadlocked with each party voting 50-50 on a law, the Vice-President can be the tie-breaker. So if Biden is elected President, a 50-50 Senate is a de facto Democratic majority and vice versa.

But such a narrow majority would be a disaster for progressives because there is a very wide range of ideological views amongst Senate Democrats and one senator in particular looms as being especially problematic: Democratic Senator Joe Manchin of West Virginia. Despite being a member of the Democratic Party, Manchin is a conservative and if his vote is needed to pass laws, very little progressive legislation will pass the Senate and it is much less likely that there will be reform of the Supreme Court.

To bypass Manchin, Democrats actually need to win a minimum of 51 seats. That could mean Iowa’s Senate seat will be critical.

So while everyone will rightly be watching the presidential race, keep your eye on some Senate seats as well. Particularly Maine and Iowa.

The data used in this post was sourced from FiveThirtyEight’s Senate forecast on Saturday 26 September. You can see the forecast here.

For a list of Senate polls by state, see here

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