A deliberate and determined effort to obstruct everything, no matter what the merits, just to refight the results of an election is not normal, and for the sake of future generations we can't let it become normal."
Like Democratic leaders in the Senate, Mr. Obama, a former senator himself, declined to characterize the rules change as a victory to be celebrated. Instead, he argued that it was a necessary move, made reluctantly, to help fix a broken system that had blocked or threatened not only nominees to the courts and his administration but also legislation on jobs initiatives, gun violence, immigration changes and women's rights.
The rule would allow a majority vote to confirm judicial and executive nominees short of the Supreme Court.
Senator Mitch McConnell, the Republican leader, denounced Democrats for trying to "break the rules to change the rules" as a way to distract the public from the president's political problems over his health care law.
(Read more: Christie's challenge: Unite divided GOP)
"You think this is in the best interest of the United States Senate and the American people?" Mr. McConnell asked, sounding incredulous. "I say to my friends on the other side of the aisle, you'll regret this. And you may regret it a lot sooner than you think."
The gravity of the situation was reflected in a highly unusual scene on the Senate floor: Nearly all 100 senators were in their seats, rapt as their two leaders debated.
Tensions between the two parties have reached a boiling point in the last few weeks as Republicans repeatedly filibustered Mr. Obama's picks to the country's most important appeals court, the United States Court of Appeals for the District of Columbia Circuit. The Senate has voted on three nominees to the court in the last month. Republicans have blocked them all, saying they would allow the president no more appointments to that court.