Sen. Lindsey Graham (R-S.C.) led a coordinated series of speeches in opposition to Paul's proposal, decrying it as a misguided effort that would undermine U.S. policy in the Middle East.
Graham sponsored the Iran resolution, with a broad coalition of supporters in both parties. His resolution prevailed, 90-1. Paul was the only Senator to vote against the measure.
"We know that Iran would create access for terrorists - access for them - to these nuclear weapons, making the Middle East a nuclear tinderbox," Sen. Richard Blumenthal (D-Conn.) said in supporting that measure. "We cannot trust this regime. We know that fact beyond any potential doubt."
Paul, on the other hand, said that the Graham resolution could have unforeseen consequences.
"I think a vote for this resolution is a vote for the concept of pre-emptive war. I know of no other way to interpret this resolution," Paul said.
The Senate's last vote before leaving for the November election season came on the sportsmen measure, which cleared a procedural vote 84-7, and will be the first order of business when the Senate returns.
Sponsored by Sen. Jon Tester (D-Mont.), who is in a tight re-election race against Rep. Denny Rehberg (R-Mont.), the bill has the backing of pro-gun and hunting groups. Before the vote, McConnell sought an agreement to take up and pass a much narrower House-approved version of the measure that would have gone straight to the president's desk, but Reid objected. McConnell then announced his support for moving forward with Tester's bill.
With the majority hanging in the balance with each Senate race - Democrats hold 53 seats while Republicans hold 47 - Reid had pledged to give Tester a vote. Tester and Democrats sensed an opportunity to gain political advantage after a sportsmen's bill sponsored by Rehberg was criticized back home for being hastily drafted.
In one final floor exchange, Reid and Minority Whip Jon Kyl (R-Ariz.) traded barbs over the scheduling of the defense authorization bill during the lame-duck session. Reid tried to get an agreement to allow the bill to reach the floor as early as November with only relevant amendments.
A visibly agitated Kyl said Reid made the request without notifying Republicans at a reasonable hour, forcing him to object. "Everybody know you can't get [the] unanimous consent of your colleagues when they're all gone," Kyl said.
Senators are not expected to return to the Capitol until about a week after the elections.
Former Sen. Scott Brown, R-Mass., candidate for U.S. Senate in New Hampshire, holds his hand over his heart during the singing of the national anthem as he waits to take the stage for his town hall campaign rally with Sen. John McCain at the Pinkerton Academy in Derry, N.H., on Monday, Aug. 18, 2014.