Aberdeen Investments has developed a machine learning election model which suggests Republicans are likely to retain control of the US Senate in November’s midterm elections, but only just.
The model, built in-house by the firm’s Global Macro team and supported by an AI-powered dashboard, combines political, economic and voter sentiment data to estimate the probability of each party winning individual Senate races. It then aggregates those state-level forecasts into an overall projection for control of the Senate ahead of the 3 November elections.
Aberdeen’s current central scenario is for Democrats to regain control of the House of Representatives, while Republicans narrowly hold the Senate. The model points to a 50-50 split in the upper chamber, leaving Vice President JD Vance with the deciding vote. It also highlights the possibility of a Democratic sweep if political momentum continues to shift in their favour over the coming weeks.
According to the firm’s research, low presidential approval ratings, weak voter sentiment and growing concerns about the economic impact of the Iran conflict have significantly reduced the likelihood of Republicans retaining outright Senate control compared with early 2025. However, the electoral map continues to give the party a structural advantage.
Bob Gilhooly, senior emerging markets economist at Aberdeen Investments, said: “Investors are often forced to navigate elections through a mixture of polling, headlines and instinct. What we’ve tried to do is create a more systematic framework that brings together political trends, economic indicators and voter sentiment to help assess how outcomes are evolving in real time.
“The story of this election is that the momentum has clearly moved against Republicans over the past 18 months. But momentum alone does not decide elections. The Senate map remains favourable to Republicans and, at this stage, our modelling suggests they do just enough to hold on.”
Lizzy Galbraith, political economist at Aberdeen Investments, said: “Midterm elections are often a referendum on the sitting president, and Republicans are facing many of the conditions that have caused incumbent parties to lose ground in previous cycles. That’s why Democrats are widely expected to take back the House.
“The more interesting question for investors is whether that political dissatisfaction is strong enough to overcome the structural advantages Republicans enjoy in the Senate. Our current assessment is that it probably isn’t, but the race is much closer than it appeared at the start of President Trump’s second term.”
For investors, Aberdeen sees a divided Congress as the most likely outcome. While gridlock could place some restraint on future fiscal expansion, the firm’s economists believe spending pressures are unlikely to disappear entirely, given the ongoing costs associated with the Iran conflict and Democratic efforts to reverse recent Medicaid cuts.
The model will continue to be updated as new polling, economic and political data become available in the run-up to election day.
