Mr. Obama introduced Judge Garland to an audience of his family members, activists, and White House staff in the Rose Garden Wednesday morning, describing him as exceptionally qualified to serve on the Supreme Court in the seat vacated by the death of Justice Antonin Scalia, who died in February.

The president said Judge Garland is “widely recognized not only as one of America’s sharpest legal minds, but someone who brings to his work a spirit of decency, modesty, integrity, even-handedness and excellence. These qualities and his long commitment to public service have earned him the respect and admiration from leaders from both sides of the aisle.”

He added that Judge Garland “will ultimately bring that same character to bear on the Supreme Court, an institution on which he is uniquely prepared to serve immediately.”

Mr. Obama said it is tempting to make the confirmation process “an extension of our divided politics.” But he warned that “to go down that path would be wrong.”

Mr. Obama demanded a fair hearing for Judge Garland and said that refusing to even consider his nomination would provoke “an endless cycle of more tit for tat” that would undermine the democratic process for years to come.

“I simply ask Republicans in the Senate to give him a fair hearing, and then an up-or-down vote,” Mr. Obama said. “If you don’t, then it will not only be an abdication of the Senate’s constitutional duty, it will indicate a process for nominating and confirming judges that is beyond repair.”

But later in the day the Senate majority leader, Mitch McConnell of Kentucky, called Judge Garland and said that the Senate would not take action on his nomination.

Mr. McConnell also informed Judge Garland that they would not be meeting in person at the Capitol on Thursday.

“Rather than put Judge Garland through more unnecessary political routines orchestrated by the White House, the leader decided it would be more considerate of the nominee’s time to speak with him today by phone,” Mr. McConnell’s spokesman, Don Stewart, said in a statement. “The leader reiterated his position that the American people will have a voice in this vacancy and that the Senate will appropriately revisit the matter when it considers the qualifications of the person the next president nominates. And since the Senate will not be acting on this nomination, he would not be holding a perfunctory meeting, but he wished Judge Garland well.”

In brief remarks in the Rose Garden, Judge Garland emotionally described his legal career as a prosecutor and a judge, saying that “fidelity to the Constitution and the law have been the cornerstone of my professional life.” He said that if the Senate confirmed him, he promised to “continue on that course.”

Ms. Garland was beaming throughout the greetings, hugging some of the most powerful people in the country. As the granddaughter of a presidential counsel, Ms. Garland is well known among this city’s elite.

In answer to a shouted question regarding her husband’s nomination, Ms. Garland shyly smiled but said nothing to reporters.

In choosing Judge Garland, a well-known moderate who has drawn bipartisan support over decades, Mr. Obama was essentially daring Republicans to press their election-year confirmation fight over a judge many of them have publicly praised and who would be difficult for them to reject, particularly if a Democrat were to win the November presidential election and they faced the prospect of a more liberal nominee in 2017.

Judge Garland persevered through a lengthy political battle in the mid-1990s that delayed his own confirmation to the United States Court of Appeals for the District of Columbia Circuit by more than a year. Senator Charles E. Grassley, Republican of Iowa, argued at the time that the vacancy should not be filled.

Twenty years later, Mr. Grassley and other Republicans are again standing in the way of Judge Garland’s appointment, arguing that the next president should be the one to pick the successor to Justice Scalia. Republicans in the Senate and on the presidential campaign trail vowed to stand firm against whomever Mr. Obama chose.

In remarks Monday, Mr. Obama chastised Republicans for taking that stand, demanding that the Republican-controlled Senate fulfill its responsibility to consider Judge Garland and hold a timely vote on his nomination. To do anything else would be irresponsible, he said.

Judge Garland is often described as brilliant and, at 63, is somewhat older for a Supreme Court nominee. He is two years older than Chief Justice John G. Roberts Jr., who has been with the court for more than 10 years. The two served together on the appeals court and are said to be friends.

Supreme Court nominees tend to be in their early 50s. In choosing Judge Garland, Mr. Obama very likely gave away the possibility of a justice who would serve on the Supreme Court perhaps three decades. Instead, he imposed a sort of actuarial term limit on the nomination and thus his legacy, offering Senate Republicans a compromise not only on ideology, but also on tenure.

The Oklahoma City bombing case in 1995 helped shape Judge Garland’s professional life. He coordinated the Justice Department’s response, starting the case against the bombers and eventually supervising their prosecution.

Judge Garland insisted on being sent to the scene even as bodies were being pulled out of the wreckage, said Jamie S. Gorelick, then the deputy attorney general.

“At the time, he said to me the equivalent of ‘Send me in, coach,’” Ms. Gorelick said. “He worked around the clock, and he was flawless.”

White House officials on Wednesday noted that Judge Garland was confirmed to his current post in 1997 with the support of seven sitting Republicans: Senators Dan Coats of Indiana, Thad Cochran of Mississippi, Susan Collins of Maine, Orrin G. Hatch of Utah, James M. Inhofe of Oklahoma, John McCain of Arizona, Pat Roberts of Kansas.

For Mr. Obama, the chance to pick a third justice for the nine-member court could also help protect his legacy by ensuring the failure of a continued legal assault on the president’s health care law, immigration actions and climate rules after he leaves office.

Some of those cases could take years to reach the Supreme Court, and a new Obama-appointed justice could provide the swing vote needed on a divided bench to keep them in place.

The president, a constitutional lawyer by training, is eager to shift the nation’s highest court away from the conservative legal philosophy that has dominated it for decades. If he succeeds, history books will show that it was Mr. Obama, more than anyone else, who reversed the judicial imprint left by the Republican presidents like Ronald Reagan, George Bush and George W. Bush.

During most of the last decade, the court has been deeply and bitterly divided. But conservatives on the bench have usually emerged victorious. Under the direction of Chief Justice John G. Roberts Jr., the court has bolstered gun and property rights while striking down voter protections and weakening campaign finance laws. It has tended to side with business interests over those of labor. And while the court legalized gay marriage last year, it has also ruled in ways that could eventually restrict college admissions based on race.

For conservatives, the fight over Mr. Obama’s nominee is perhaps the most critical moment in their almost decade-long crusade to defend their ideological influence. From the day Mr. Obama was inaugurated in 2009, conservatives vowed to keep him from changing Washington, as he pledged during his campaign. Preventing another Obama justice on the Supreme Court is vital to that mission.

(Published by The New York Times - March 16, 2016)