WASHINGTON — Nearly 16 years to the day after Congress first authorized a military response to the attacks of Sept. 11, 2001, the Senate on Wednesday rejected an effort to repeal the virtual blank check that Congress granted to the president while smoke still rose from the rubble of the World Trade Center.

The debate pitted the Republican Party’s ascendant isolationist wing, represented by Senator Rand Paul of Kentucky, against its old-line interventionists, led by Senator John McCain, Republican of Arizona, who is pressing his vision of a muscular military even as he battles brain cancer.

Mr. Paul pressed for the repeal vote, in a strange bedfellows alliance with Senator Tim Kaine, the Virginia Democrat who was his party’s vice-presidential nominee last year. But the effort failed when senators voted 61 to 36 to set the measure aside, rather than include it in the annual defense policy bill that senators are considering this week.

“What we have today is basically unlimited war — war anywhere, anytime, any place on the globe,” Mr. Paul told his colleagues in a speech Tuesday afternoon on the Senate floor. “I don’t think anyone with an ounce of intellectual honesty believes these authorizations allow current wars we fight in seven countries.”