President Donald Trump is on the cusp of another potential setback from Congress in the war against Iran, and it could come at the hands of one of the Republicans he’s forcing into retirement: Sen. Bill Cassidy (R-LA).

The Senate heads into an uncertain vote Thursday on its latest attempt to end the conflict and require congressional approval following U.S. troop casualties. The math couldn’t be tighter for what will mark the 12th vote this year on a bipartisan Iran war powers resolution.