The U.S. Senate failed to pass legislation that would have barred President Donald Trump from launching an attack on Iran without first obtaining congressional approval.
Senators voted 50-to-40 in the June 28 vote, falling short of the 60-vote minimum in the Republican-controlled Senate to pass the amendment.
The measure was attached to the annual policy bill known as the National Defense Authorization Act, which passed the chamber a day earlier.
But Senate leaders then decided to allow the amendment after several Republicans joined Democrats in calling for debate.
The legislation came as tensions between Washington and Tehran have spiked.
Last year, Trump withdrew the United States from a 2015 nuclear deal that sought to curb the Iran's nuclear program in exchange for an easing of sanctions.
He has since reimposed economic sanctions on Tehran.
In recent months, Trump has ordered an increase in U.S. forces in the Middle East, and deployed a U.S. aircraft battle group to the region.
Last week, Trump said he made a last-minute decision calling off air strikes in response to Iran's downing of a U.S. military drone
Supporters of the legislation said it was necessary to ensure that Congress exercises its constitutional right to authorize the use of military force.