The University of Michigan Consumer Sentiment Index has fallen from 56.4 in January to a preliminary reading of 48.2 in May, placing it near historic lows associated with recessionary and stagflationary periods.

The significance of the decline is not merely economic. In American politics, voters tend to judge administrations less on headline GDP figures and more on what they experience at petrol stations, supermarkets, and in monthly household budgets. Historically sentiment readings below 70 have coincided with severe electoral punishment for incumbent administrations.

The current reading of 48.2 places Republicans in territory historically associated with major midterm losses.

The key driver has been energy. Rising oil prices linked to the Iran conflict have fed directly into higher fuel costs, which in turn have driven broader inflation pressures. There is also an apparent detachment between consumer sentiment and actual inflation data. The April Consumer Price Index (CPI), a measure of inflation, reached a moderate 3.8% - a number that belies the increasingly pessimistic sense amongst Americans about their purchasing power. Some analysts have even advised that the CPI number is no longer an appropriate measure from which to judge consumer pressure.

That creates a growing problem for President Donald Trump.

His administration’s strategic problem is that it likely cannot materially improve consumer sentiment without lowering oil prices. Yet the Iran conflict is doing the opposite. Every additional month of elevated energy prices deepens pressure on household finances and reinforces the sense that the administration has lost control of inflation.

That means Trump is running short on time to engineer an exit or de-escalation from the Iran war sufficient to bring crude prices down before the political damage becomes entrenched ahead of November.

Last week’s meetings with China may also not have produced the inflection point the White House had hoped for. While the talks lowered immediate fears of direct confrontation between Washington and Beijing, they did not appear to deliver the hoped for pressure from China to get Iran to come to terms with the United States on nuclear questions. The Iranians appear to have been emboldened by that to hold out against American pressure.

At a strategic level that makes sense as both Tehran and Beijing would see an upside in a weakened Trump administration and would both welcome Democrat control of Congress.

The danger for Republicans is therefore that the midterms increasingly become a referendum not on abstract geopolitical strength, but on whether ordinary Americans feel poorer than they did six months ago.

At present, the data suggests they do.