Responsible Statecraft has reported:

Republicans could face a major setback in November’s midterm elections, with the Iran war adding pressure to an already difficult contest for control of Congress. Democrats are leading in nearly all the Senate races considered toss-ups, including contests in the reddest states, and are competitive in at least a dozen races that will determine control of the chamber. The Senate was not expected to be in play, while Republicans’ narrow House majority was always considered vulnerable.

The war has weakened support among parts of President Donald Trump’s coalition that were less firmly partisan and expected him to avoid new prolonged conflicts in the Middle East. It has also displaced the focus on affordability that many voters anticipated after Republicans defeated Democrats in 2024. Higher energy prices and broader inflation have added to the cost-of-living concerns that voters have carried for years.

The conflict has virtually no support among Democratic voters and is opposed overwhelmingly by independents. A significant group of Republicans was never in favour of it, while many who supported the war expected it to end quickly, as Trump repeatedly said it would.

Trump appeared ready to end the war by June, but has not restored the Strait of Hormuz to its pre-war status. His efforts have included escalations, ceasefires and negotiations. One effort ended with a memorandum of understanding signed by Iran and the United States on June 17 that did not succeed.

The president made no sustained effort to persuade the public to support the war. He did not address Iran in a pre-Christmas prime-time speech last year that was intended to signal a shift toward the economy, and barely mentioned the Islamic Republic in his State of the Union address. His first prime-time address about the war came more than a month after it began. He also did not seek congressional authorization for the use of force, despite Republicans holding both chambers.

Republicans were likely to lose congressional seats even before the conflict. Since 1938, midterm elections have generally favoured the party that does not hold the White House. Some voters in Trump’s coalition are less likely to turn out when he is not on the ballot, while people opposed to Trump can be expected to cast protest votes against Republicans.

Before the war, however, Democrats could still have ended up with a modest result, similar to Republicans’ performance in Joe Biden’s 2022 midterms. The blue wave might have been limited, as the anticipated red wave was then. Eighty-six per cent of House Republicans represent districts Trump won by at least 10 percentage points. Republicans sought to strengthen that position through mid-decade redistricting in red states. The Senate path also ran through states Trump carried in 2024, often by double-digit margins.

The war has raised the possibility of a midterm result more like 2006. Cook Political Report’s Amy Walter drew a comparison earlier this year to that election, which took place during an unpopular war under an unpopular president, as Republican congressional incumbents faced various scandals. That year, the Iraq war had been under way longer and had caused more American casualties by the time voters went to the polls.

Today, public patience with the Iran war is even thinner, the source argues. Republican candidates in close races have already qualified their support for it more quickly than their counterparts did over Iraq two decades ago. Michigan Republican Senate candidate Mike Rogers, a hawkish contender in one of the country’s most competitive races, said in a September campaign ad: “The war with Iran needs to end, and end quickly,” Rogers said. “Michigan families can’t afford to wait.”

The economic burden is apparent even to supporters who remain behind the war. It is landing on voters who have been frustrated with high living costs for at least five years. During George W. Bush’s second term, the combination of Iraq and the 2007-08 economic crisis eventually weakened his standing among congressional Republicans. The source argues that existing economic conditions and Trump’s strained relationship with the remaining old Republican establishment have brought that reckoning forward in the case of Iran.

If Republicans fare badly in November, many may blame tariffs instead of the war. Tariffs and their uneven implementation are a substantial part of the political problem and can be more directly attributed to Trump and the MAGA movement. Those policies and the assumptions behind them may be easier to remove from the party than interventionism, which has been rooted in the Republican Party for a long time and was supposed to be displaced by Trump.

The war has also raised costs beyond imported goods, highlighted what the source describes as Trump’s lack of attention to domestic concerns in his second term, and increased the effect of tariffs on household budgets. The two issues may therefore reinforce one another rather than operate as separate explanations for voter frustration.

The conflict has complicated the position of Vice-President JD Vance, who, according to many accounts cited in the source, was the senior administration official most sceptical of starting the war. Trump had brought together Republicans with different foreign-policy views by appearing to recognize the limits of what the United States had tried to accomplish in the Middle East over the previous quarter-century, while not seeming hostile to Israel or afraid of regional adversaries.

After the Iran war, Republicans who favour a less interventionist foreign policy may press Vance to criticize neoconservatives or Israel more directly, potentially deepening party divisions. Hawks may target him because they do not see him as one of their own. Doves may also hold back from defending him because they have doubts about his position.

Two Kentucky Republicans could offer an antiwar challenge in a primary: Sen. Rand Paul or Thomas Massie, who is soon to be a former congressman. Both built their congressional careers on the movement-building presidential campaigns of former congressman Ron Paul, Rand Paul’s father. Massie has little chance of winning a nomination for the same reasons he lost his congressional primary earlier this year, though either candidate could conceivably help rebuild the Republican Party’s libertarian wing, which the source describes as being in disrepair. Both are unlikely to run such a campaign.

Vance could benefit if neoconservatives attack him as too dovish while libertarians criticize him as too hawkish. That pressure might help him persuade ordinary Republicans that he occupies a middle position. He has displayed political skill in managing his relationship with Trump. Secretary of State Marco Rubio, Vance’s most frequently cited potential rival, is also closely tied to the administration and more closely associated with the assumptions behind the Iran war, even if not necessarily with the decision to launch it.

The conflict could be over by 2028 and remembered by Republicans as a lesson that the party had reached its limit with a pro-war stance. Trump and former president George W. Bush each had significant political opportunities to pursue wars in the Middle East, and the resulting conflicts cost the party its congressional majorities. The source cautions that neither an end to the war nor a lasting change in Republican policy is assured. The party’s structural electoral advantages could still soften the losses that now appear possible in November.