In a letter to fellow senators, Bennet described the war as President Donald Trump's "short-sighted misadventure" and said it has driven up the cost of gas, groceries and fertilizer. He framed the coming spending fight as a test of whether Congress will listen to voters.

"We return to the Senate with clear direction from the American people," Bennet wrote. "Together, we must bring President Trump's disastrous war with Iran to an end."

Bennet noted that the continuing resolution funding the government and the war expires on Dec. 11, and he urged senators to block any additional funding packages. He said he will vote against any such resolution.

His stance marks a break with his own past votes. Last year, Bennet voted against the National Defense Authorization Act for the first time in his career, citing what he called Trump's reckless foreign policy and a "lawless" Department of Defense under Secretary Pete Hegseth.

"The stakes are too high for us to fall into our usual shutdown politics," Bennet wrote. "Instead, we should act in a bipartisan manner to forcefully reject the Administration's request for additional funding for the Iran war, a war Congress never authorized and the American people do not want."

Bennet is not alone among Colorado lawmakers in voicing concern. Republican U.S. Rep. Lauren Boebert, a staunch Trump ally who represents Colorado's 4th Congressional District, announced last spring that she would no longer support additional war funding. In a CNN interview, she said she had told leadership she is "a no on any war supplementals."

"I am so tired of spending money elsewhere," Boebert said. "I am tired of the industrial war complex getting all of our hard-earned tax dollars. I have folks in Colorado who can't afford to live."

During a debate last month against Democratic challenger Eileen Laubacher, Boebert said she "never wanted" the country involved in the war but stood by Trump's decision as commander in chief. She said she hears from Republicans, unaffiliated voters and Democrats who want the conflict to end.

"I do agree that this is expensive, and I hear from Republicans, unaffiliated (voters), and Democrats that they want this to come to an end, and so do I," Boebert said. "We are having conversations with the Department of War and with the president on a regular basis about how to come to an end with this."

The war and its effect on the cost of living became a central issue in the midterm elections, in which Democrats flipped more than three dozen Republican-held seats and won control of the U.S. House of Representatives. Vice President JD Vance blamed the war for the results, writing on his personal X account on Nov. 4 that "the reason we lost is the war. The president said so last night."

With the Dec. 11 funding deadline approaching, Bennet's letter signals that the fight over war funding will shape the lame-duck session and test whether Congress will assert its authority over a conflict it never formally authorized.