Democrats won Congress. Should UK investors change their portfolios?

Democrats have won the US House of Representatives and the Senate. If you hold a diversified portfolio and your plans are much as they were before the election, I see little reason to change what you own on the strength of that result alone.

The S&P 500 rose 1.6% in dollar terms on Wednesday 4 November, the first trading day after the vote. Yet some US data-centre shares fell that same day. An investor holding a broad US index and one whose wealth was tied up in a handful of those companies had quite different Wednesdays. How the Associated Press called Congress · Reuters’ market report.

What changes with a Democratic Congress?

When the new Congress takes its seats in January, President Trump will face Democratic majorities in both chambers. That changes who sits across the table in negotiations over taxes and public spending. For a business relying on a federal contract or a particular tax credit, the outcome of those negotiations can matter a great deal.

As an investor, though, you’d need to get two things right to profit from that insight. You’d need to anticipate the policy that actually becomes law, then judge whether today’s share price already allows for it. Someone who correctly called the election could still buy the wrong company, or pay too much for the right one.

What have US shares returned under divided government?

Janus Henderson used Bloomberg data to compare the S&P 500 under two arrangements. In one, the same party held the presidency, House and Senate. In the other, power was divided. Over the 50 years to 23 October 2026, the difference in annualised share price returns was just over half a percentage point.

Look at what went into those averages. The divided-government figure covers 32 years and the unified-government figure covers 18. Investors lived through different interest rates, company profits and starting valuations in each period. I’d be wary of treating the 0.51 percentage point gap as a reward you can collect whenever Washington changes hands.

There’s a separate question about timing. US shares have often done well around midterms. Researchers who examined 49 US industry portfolios from 1926 to 2022 found that most of the apparent advantage disappeared once they allowed for the risk investors took. That gives me little basis for moving clients into cash before an election and trying to buy back afterwards.

What does it mean if you spend pounds?

Imagine a couple drawing £40,000 a year from their investments to supplement their pensions. They want £10,000 in January. The most useful question I could ask them this week is a simple one. Where will that £10,000 come from?

If it’s already set aside in sterling, they can meet that withdrawal without selling US shares at whatever price happens to prevail in January. If the whole payment depends on selling an unhedged US equity fund, they are relying on both share prices and the exchange rate. Even if the shares stand still in dollars, a 5% fall in the pound value of each dollar would turn a £10,000 holding into £9,500 before charges. Vanguard explains how currency hedging works.

In that situation I’d work backwards from the January withdrawal. I’d use cashflow planning to map their forthcoming withdrawals and decide how much spending to cover in sterling. A younger investor paying into a pension each month has a different timetable and may have no near-term call on the money at all.

When would I change the portfolio?

I’d act if a review uncovered something that mattered to the investor. Perhaps years of strong US share returns have taken equities above the allocation we agreed. Perhaps shares in a former employer now account for much of the money earmarked for retirement. Or perhaps the family wants to help a child with a house deposit two years sooner than planned.

Each gives me a reason to consider rebalancing, reducing a concentration or setting aside cash. If the mix of assets still fits the job the money has to do, I’m comfortable leaving it alone. You can read more about how I manage investment portfolios.

This is general investment commentary. Investment values can fall as well as rise, and past performance is an unreliable guide to future returns.

Capitol photograph by Noclip, Wikimedia Commons (public domain).