WASHINGTON >> Nearly 16 years to the day after Congress first authorized a military response to the attacks of Sept. 11, 2001, the Senate today 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 Sen. Rand Paul of Kentucky, against its old-line interventionists, led by Sen. John McCain, R-Ariz., who is pressing his vision of a muscular military even as he battles brain cancer.

Paul pressed for the repeal vote, in a strange bedfellows alliance with Sen. Tim Kaine, the Virginia Democrat who was his party’s vice-presidential nominee last year. But the effort failed when senators voted 61-36 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,” 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.”

Paul had proposed repealing the declaration in six months, to give lawmakers time to consider a new one. The issue has been around since 2015, when President Barack Obama asked Congress to replace the authorization of military force passed to battle al-Qaida with a new one crafted specifically to take on the Islamic State.

But so far Congress has balked, declining to take on the difficult issue even as lawmakers such as Kaine insist that the legislative branch should reclaim its constitutional duty to declare war.

In the House, in another unlikely partnership, Rep. Barbara Lee, the California Democrat who was the only member of the House to vote against the original resolution in 2001, paired up with Rep. Scott Taylor, a freshman Virginia Republican and former Navy SEAL, over the summer to convince the Appropriations Committee to insert language repealing the original use of force declaration into a spending bill.

“I just felt compelled to stand up and say, now it’s time to look at the AUMF,” Taylor said, using the acronym for the authorization for the use of military force. He said once he spoke up, other Republicans joined in to support him: “It’s an issue that I don’t think is going to go away.”

But Republican leaders stripped the provision out of the spending measure; Speaker Paul D. Ryan said at the time that the move was a “mistake” and that such language was not appropriate for inclusion in a spending measure.

“It was really shameful,” Lee said in an interview. “The Constitution requires us to do our job and debate the costs of war.”

Wednesday’s vote put the question of the president’s authority to commit troops overseas up for a vote for the first time in a generation, and some lawmakers, mindful of their obligations under the Constitution, seemed genuinely torn.

Sen. Jack Reed of Rhode Island, the senior Democrat on the Armed Services Committee, said that in forcing senators to take a stand, Paul had “been relentless in doing something that has to be done.”

But, he added, “You can’t replace something with nothing, and we have nothing.”

Sen. Mitch McConnell of Kentucky, the Republican leader, argued strongly against repealing the military force authorization, saying that ending the authority the president relies on to fight the Islamic State would create only confusion within the armed forces.

“We have an all volunteer force that protects all of us and fights for us,” McConnell told his Senate colleagues, adding, “We cannot break faith with these men and women by removing the authority they rely on to pursue the enemy.”

Wednesday’s vote cleared the way for the Senate to begin work on a massive $700 billion defense policy bill, championed by McCain, chairman of the Senate Armed Services Committee.

The bipartisan defense bill, approved by the Armed Services Committee on a unanimous 27-0 vote, is considered a must-pass piece of legislation — in part because the annual measure has been approved by Congress each year for more than half a century, and in part this year for sentimental reasons; it is deeply important to McCain.

The defense measure sets forth McCain’s interventionist vision of America’s role in the world — a vision very different than that of the isolationist Paul, or President Donald Trump. It includes $37 billion more in funding for the Pentagon than Trump asked for, authorizes $500 million to provide “security assistance,” including weapons, to Ukraine; $100 million to help Baltic nations “deter Russian aggression” and $705 million for Israeli cooperative missile defense programs — $558.5 million more than the administration’s request.

“It’s a grandiose spending plan,” said Sen. Dick Durbin of Illinois, the Democratic whip. “We expect it each year. He challenges us to move toward his direction, and usually has his way to some extent.”

McCain said he is using the measure to send a message to the president about the role of Congress: “We are a co-equal branch of government.”

But before the Senate could move to the defense policy bill, it had to deal with the demand for the use of force vote from Paul. He and McCain have been at odds for years; McCain once called Paul a “wacko bird,” (though he later apologized) and Paul called McCain “unhinged” and “past his prime” in an interview earlier this year.

McCain had hoped senators could begin considering the defense bill in July, shortly after his dramatic thumbs-down vote that killed a repeal of the Affordable Care Act. But Paul exercised his authority to block the bill from coming up for a vote, demanding that his use of force measure be attached as an amendment. McCain refused.

Congress first granted the president authority to use force on Sept. 14, 2001, just three days after the terrorist attacks; the following year, with President George W. Bush threatening war against Iraq, a second use of force resolution was approved. The Trump administration, like the Obama administration before it, has claimed legal authority to wage war against the Islamic State under the initial authorization.

Paul has for years been pushing for a repeal of both resolutions, arguing that Congress never intended them to serve as the underpinning to combat operations in countries from Yemen to Somalia, much less against the Islamic State, which did not exist when the initial declarations were approved.

Three-quarters of the members of Congress — including both Paul and Kaine — had yet to be elected when Bush signed the declarations into law.

“The current interpretation of the authorization essentially allows an American president, without any approval from Congress, to wage war anywhere against any terrorist groups for however long they want to,” Kaine said in a speech Tuesday afternoon on the Senate floor.

Both men argue that, in not reconsidering the force declarations, lawmakers are shirking their responsibilities under the Constitution, which grants Congress “the power to declare war and raise and support the armed forces.” But Republican and Democratic leaders have been reluctant to take up the issue — wary of having to explain a vote granting the president war powers to constituents in a war-weary nation.

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