As part of the United States Senate Committee on Foreign Relations in 2018, Lee, Bernie Sanders, and Chris Murphy co-sponsored a resolution "that would end U.S. military support for the Saudi-led campaign in Yemen's civil war". Interviewed by "The Hill", he said: "regardless of what may have happened with Mr. Khashoggi, we are fighting a war in Yemen that we haven't declared, that has never been declared or authorized by Congress. That's not constitutional." The Senate voted 60–39 to "formally begin debate on the resolution", which would require the President to "withdraw troops in or 'affecting' Yemen within 30 days unless they are fighting al Qaeda".