President Obama has nominated Merrick Garland to serve on the Supreme Court. Here is what you need to know about Garland. (Claritza Jimenez,Gillian Brockell/The Washington Post)

President Obama nominated Appeals Court Judge Merrick Garland to the U.S. Supreme Court on Wednesday, calculating that the highly regarded jurist might blunt some of the expected political attacks and ultimately embarrass Senate Republicans into dropping their fierce opposition to the nomination.

Amid a swirl of speculation about whether Obama would use the vacancy to expand ethnic or gender diversity on the court, Obama picked Garland, the 63-year-old chief judge of the U.S. Court of Appeals for the District of Columbia Circuit. A moderate who has been on the appellate bench for almost two decades, Garland has served presidents from both parties and was confirmed by the Senate 19 years ago. He is the grandson of Jewish immigrants from Eastern Europe, not a “first” in the way an Asian American or black female nominee would have been.

But Obama decided that it might be more politically difficult for Republicans to deny Garland a hearing and a vote after he has been the subject of effusive bipartisan accolades for decades.

“I hope they’re fair,” the president said of Senate Republicans during his Rose Garden announcement. “That’s all. I hope they are fair.”

Although Obama was composed and even a bit defiant in his remarks, Garland choked up as he thanked the president. “This is the greatest honor of my life — other than Lynn agreeing to marry me 28 years ago,” Garland said. He mentioned his mother watching on television and “crying her eyes out” and his two sisters, “who have supported me in every step I have ever taken. I only wish that my father were here to see this today.”

In private conversations with aides and political allies in recent days, the president emphasized that although he might have disappointed some supporters who were lobbying for a woman or a person of color, he picked someone with whom he has a personal affinity and someone whose record was, in Obama’s words, “unassailable.”

White House senior adviser Valerie Jarrett said in an interview that Obama “was looking for someone whose values he shares, who’s committed to public service” and could serve as “a consensus builder” on the court.

“There is a humanity to his character that touched the president, as well,” she added.

Garland was on a list of three finalists that also included Sri Srinivasan, a 49-year-old Indian American who also sits on the D.C. Circuit, and Paul Watford, a 48-year-old California judge on the U.S. Court of Appeals for the 9th Circuit.

After the announcement, Senate Republican leaders reiterated their intention not to vote on the nomination, arguing again that they think the next president should fill the vacancy because it comes in the middle of a presidential election season and so late in Obama’s final term. But they refrained from attacking Garland directly. Half a dozen said they would meet with him, and a couple said they would consider holding a vote during a lame-duck session, especially if a Democrat won the White House in November.

Garland, who was appointed to the D.C. federal appeals court by President Bill Clinton in April 1997, was confirmed on a 76-to-23 vote and became chief judge three years ago. Seven current Republican senators voted to confirm Garland to the federal bench in 1997: Daniel Coats (Ind.), Thad Cochran (Miss.), ­Susan Collins (Maine), Orrin G. Hatch (Utah), James M. Inhofe (Okla.), John McCain (Ariz.) and Pat Roberts (Kan.).

Everything you need to know about appointing a Supreme Court justice

Senators of both parties settled in Wednesday for what all expect to be an extended political siege around the nomination. Democrats will seek to pressure vulnerable Republican incumbents in tough reelection campaigns — and by extension, GOP leaders who are hoping to preserve their Senate majority — into abandoning the blockade.

Senate Majority Leader Mitch McConnell (R-Ky.) vowed that will not happen.

“It seems clear that President Obama made this nomination, not with the intent of seeing the nominee confirmed, but in order to politicize it for purposes of the election,” he said. “The American people are perfectly capable of having their say — their say — on this issue. So let’s give them a voice.”

Later in the day, McConnell spoke by phone with Garland and, according to McConnell’s spokesman, “wished Judge Garland well” but made clear he would not meet with him.

But several other GOP senators, including some who are up for reelection, said they would meet with Garland. “I meet with people; that’s what I do,” said Sen. Jeff Flake (R-Ariz.), a Judiciary Committee member.

Several Democrats said they did not think that Republicans would be able to maintain their opposition over the long term, especially as Donald Trump continues his march toward the GOP presidential nomination. At the very least, several postulated, they would be forced to relent in a lame-duck session if a Democrat wins the presidency in November.

“Republicans are underestimating how awful it is going to be when they go back home for their recess,” said Sen. Brian Schatz (D-Hawaii). “If you’re here in Washington for too long, you might be mistaken and misled into thinking this is a partisan issue. When they go back home, they’re going to get an earful.”

While Democratic-aligned activist groups had pushed for a more uniformly liberal nominee — and one who would make the court more diverse — virtually all Democratic senators who addressed Garland’s nomination said they were pleased by the choice.

“Nobody questions this man’s qualifications,” said Sen. Patrick J. Leahy (Vt.), the top Judiciary Committee Democrat.

Ed Whelan, a former Republican aide to the Senate Judiciary Committee who is now president of the Ethics and Public Policy Center and is advising conservative groups opposed to the Obama nomination, said Garland’s nomination seemed calculated to “crack the Republican line.”

“Most justices are able to time their departure from the court so that someone of similar ilk replaces them,” he said. “My guess is the White House decided that rolling the dice, that they had the best chance of getting action on the Garland confirmation.”

By Wednesday evening, there were cracks in the GOP wall, but only a few.

Senate Judiciary Committee Chairman Charles E. Grassley (R-Iowa) did not mention Garland by name, but in a lengthy statement he defended the Senate’s right to withhold its consent. “The American people shouldn’t be denied a voice,” he said.

After an afternoon call with Garland, he did not rule out a meeting but said if one were scheduled, he would only reiterate his determination to save the nomination for the next president.

After making his formal announcement, Obama met with the leaders of 23 progressive advocacy groups representing issues including labor, civil rights, abortion rights and the environment in the Roosevelt Room. Participants in the meeting with the president, who spoke on the condition of anonymity in order to speak frankly, said Obama emphasized that he did not pick a nominee with an eye to pleasing a specific political constituency. He said he thought many Americans would see the inherent unfairness of Republicans’ denying Garland a hearing.

Obama said that despite “a political season that is even noisier and more volatile than usual,” he hoped lawmakers would take the nomination seriously. “I chose a serious man and an exemplary judge,” he said.

Democrats on the campaign trail are hoping to leverage the court nomination as part of a broader narrative about Republican resistance to the president’s policies.

Both Hillary Clinton, the Democratic presidential front-runner, and her rival, Sen. Bernie Sanders of Vermont, called on the Senate to vote on Garland. Clinton hailed Garland as “a brilliant legal mind” with a long history of “bipartisan support and admiration.” Refusing to consider the nomination would be “entirely unacceptable,” she said.

If the Senate declines to take up Garland’s nomination before Obama leaves office, or votes it down, the next president will have the option of resurrecting the nomination or choosing someone else to fill the vacancy on the Supreme Court. Either way, the process would begin anew with the next Congress.

Sixty-three percent of Americans said the Senate should hold hearings on Obama’s nominee to replace the late justice Antonin Scalia, while 32 percent said it should not hold hearings and leave it to the next president, according to a Washington Post-ABC News poll released last week.

Administration officials are hopeful that the GOP senators who are most vulnerable this November — Sens. Kelly Ayotte (N.H.), Ron Johnson (Wis.), Mark Kirk (Ill.) and Pat Toomey (Pa.) — may lobby their leaders for a vote if they come under fire back home for blocking the nominee.

William Branigin, Mark Berman, Jerry Markon, Anne Gearan and Robert Barnes contributed to this report.