Several Republicans who attended said Trump engaged in a shouting match with senator Bill Cassidy, who said the administration needed to explain a framework deal Trump signed that gives Iran financial incentives but falls short of the goals he laid out at the war's beginning.
"The American people need to know more than we are being told," Cassidy told reporters on Wednesday.
"It does not appear, although I don't know for sure, that the course of this is going the way that we were told."
Later, in an effort to please the president, the Senate's Republican leaders scheduled a late-night vote to block a resolution calling for an end to hostilities with Iran.
The Senate voted by 50 to 47, largely along party lines, to block a war powers resolution that had advanced on a procedural vote in May.
"This vote puts Iran on notice," Trump said on social media.
Wednesday's high-volume lunchtime exchange with a member of Trump's own party shows how the war has weighed on the president before November elections that will determine control of Congress.
With Trump's approval rating at its lowest since he returned to office in 2025, just one in four Americans believes the war was worth its costs, a Reuters/Ipsos poll showed.
The exchange came a day after the Senate voted to direct Trump to end the war in a separate vote on a nearly identical resolution passed by the House of Representatives in June.
Cassidy was one of four Republicans to back it, along with opposition Democrats.
Several hours later, the administration asked Congress for $US70 billion ($A102 billion) to cover the cost of the war, adding to the US military budget of $US867 billion.
In a Wednesday evening post on X, Cassidy thanked Vice-President JD Vance and special envoy Steve Witkoff for a "thorough briefing" on Iran "to address many of my concerns".
Benchmark oil prices fell on Thursday to their lowest since before the war started as the initial accord between the US and Iran lifted Iran's chokehold on the Strait of Hormuz, allowing traffic to flow again.
Before the waterway was blockaded in the war, it had carried one-fifth of global oil and liquefied natural gas shipments.
Conflicting accounts have emerged over elements of the framework deal, which has prompted criticism of Trump at home and abroad.
Financial incentives for Iran, inspections of its nuclear facilities, control of the strait and Israel's parallel war in Lebanon have been disputed.
The deal sets up 60 days of talks to tackle thornier details, such as Iran's nuclear program.
The proposed peace deal has provoked scepticism in the Middle East, where many states came under attack from Iran during the war and view the accord as too generous to Tehran, including a $US300 billion fund and the waiver of some sanctions.
The accord also does not address Tehran's ballistic missile capacity.
The deal requires Iran to let shipping flow freely through the Strait of Hormuz for 60 days, and Tehran has suggested it might impose tolls after that - something Washington and its Gulf allies oppose.
In Washington, Lebanon and Israel discussed a US-backed proposal for Israel's forces to pull out of some territory it invaded to be handed back to Lebanese army control.
But Israeli Prime Minister Benjamin Netanyahu said Israel would not pull troops out.
Israel has been battling Hezbollah in Lebanon since the militant group attacked Israel on March 2 in support of Iran, and Tehran has made a cessation of hostilities there central to its demands in any peace deal with the US.
