Just when Republicans thought they’d caught a break on gas prices, the collapse of President Trump’s Iran deal is derailing their best chance to change the inflation story before the midterms.

Why it matters: Falling gas prices are one of the most tangible ways to ease voter anger over inflation. Renewed combat — and the threat of escalation — has prices shooting back up.

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The big picture: Trump has said repeatedly that gas prices will “drop like a rock” when the war is over. But the war doesn’t look like it’s ending anytime soon.

• When the U.S. first launched attacks on Feb. 28, average gas prices nationally were $2.98 a gallon, per AAA. They eclipsed $4.50 in May, gradually dropped to about $3.75 earlier this month, and are now flirting with the $4 mark since combat broke out again.

Zoom in: Surprisingly, Americans typically don’t punish politicians for their own economic suffering; instead, they tend to look at how government policies are affecting the country overall.

• But gas prices are a different story, says Stanford’s Jon Krosnick, who’s studied how they affect politics.
• “It’s hard to think about any other economic indicator where the number is literally posted on signs on the streets where everybody’s traveling,” he told Axios.

Zoom out: Krosnick, in a 2016 study looking at three decades of evidence, found that a 10-cent increase in gas prices caused a 0.6% drop in a president’s approval ratings. He said the effect extends to the president in power’s party.

• Unlike other instances where presidents could blame other global factors, it’s clear in this case that Trump owns the war.
• And Iran’s unwillingness to open the Strait of Hormuz shows he can’t dictate events like he’s used to.
• “If the strait stays closed, he could be in deep trouble in the election,” says Desmond Lachman, a senior fellow at the American Enterprise Institute and former International Monetary Fund official. “Iran knows it can cause real damage to the economy before the election.”
• Nearly eight in 10 Americans say gas prices are straining their household budgets, according to a PBS/NPR/Marist poll last month.

Context: The Republican-controlled Congress approved a housing affordability bill that Trump panned. Otherwise, the GOP has little to point to on the subject of voters feeling squeezed by higher prices.

• Trump has fixated on unproven allegations of voter fraud, rather than inflation and the economy.
• “I think oil is going to be a little bit of a yo-yo. Goes up a little bit, goes down a little bit,” Trump told Fox Business last week. “And when this is over oil is gonna drop like a rock.”

Yes, but: The status of the war changes constantly. With almost four months until the election, conditions in Iran could shift in a way that causes gas prices to fall again in time for Republicans to benefit.

• “Long-term trends matter, but short-term trends also matter,” Krosnick says.

The bottom line: As gas prices go, so may GOP hopes in the midterms.