WASHINGTON (Reuters) - President Barack Obama is considering appointing a moderate Republican to the Supreme Court, a source close to the process said on Wednesday, but leaders in the Republican-led Senate held firm to their threat to block anyone he nominates.

The source said Nevada Governor Brian Sandoval, a Republican and former federal judge, was among the possible candidates.

As governor, Sandoval has taken a traditional Republican stance in support of gun rights, but his more moderate views on social issues, such as abortion rights, could make him an attractive choice for the Democratic president.

A 52-year-old Mexican-American, Sandoval was appointed a judge by Republican George W. Bush, Obama’s predecessor, before being elected governor in 2010. He abandoned his state’s legal defense of a same-sex marriage ban before the Supreme Court declared such bans unconstitutional last year.

The Feb. 13 death of long-serving conservative Justice Antonin Scalia created a vacancy on the nine-seat court and ignited a political fight. Republicans are maneuvering to foil Obama’s ability to choose a replacement who could tilt the court to the left for the first time in decades. Scalia’s death left the court with four liberals and four conservatives.

Senate Majority Leader Mitch McConnell announced on Tuesday the Senate will not hold hearings or vote on any Supreme Court nominee until the next president takes office in January 2017, following the Nov. 8 presidential election. Republicans hope to win back the White House then.

The Senate must confirm any high court nominee, but McConnell remained unswayed even with word that Obama was considering the Republican Sandoval for the job.

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“This nomination will be determined by whoever wins the presidency in the fall,” McConnell said.

Senator Chuck Grassley, chairman of the Judiciary Committee that would hold any confirmation hearings, concurred, saying, “It’s the principle, not the person.”

The White House said it was hoping for a meeting with Grassley and his committee’s top Democrat, Patrick Leahy. A McConnell aide said McConnell was trying to schedule a meeting with Obama to reiterate his opposition to any nominee.

‘HE WAS INTERESTED’

Sandoval met on Monday in the U.S. Capitol for about 30 minutes with Senate Democratic leader Harry Reid of Nevada, and Reid asked him whether he would be interested in being considered for the high court job, according to the source, who asked not to be identified.

“He said he was interested,” the source said of Sandoval, adding that “a number of people are being checked out” for the job. Reid is a close ally of Obama.

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White House spokesman Josh Earnest declined during a briefing to confirm whether Sandoval was on Obama’s list of potential nominees.

White House officials are seeking a candidate they think lawmakers from both parties could support, but Obama may be unlikely to choose any Republican, even a centrist. The Democratic political base would object to such a choice, a risk Obama is unlikely to take during an election year.

Some liberal groups expressed alarm that Sandoval would be considered. Charles Chamberlain of the group Democracy for America called it “downright absurd” that Obama would risk his legacy by appointing “another anti-labor Republican” to an already pro-big business Supreme Court.

Sandoval opposed Obama’s healthcare law, but opted to expand his state’s Medicaid health insurance program for the poor under the measure, breaking from a number of Republican governors who refused to do so.

He expressed support for bipartisan immigration legislation that passed the Senate in 2013 before dying in the House of Representatives amid Republican opposition.

In 2013, Sandoval vetoed legislation to require background checks on all Nevada gun sales. Last year, he signed a law backed by the National Rifle Association that expanded the defenses for justifiable homicide and repealed a local ordinance that required handgun registration.

‘WORTHY TO SIT’

Obama vowed on Wednesday to move ahead with a nominee and said Republicans would risk public ire if they blocked a qualified candidate for political motives, as well as diminishing the credibility of the high court.

Obama said he expected the Senate Judiciary Committee to extend his nominee the courtesy of a confirmation hearing and then vote on whether he or she is qualified.

“In the meantime, the American people are going to have the ability to gauge whether the person I’ve nominated is well within the mainstream, is a good jurist, is somebody who’s worthy to sit on the Supreme Court,” Obama told reporters in the Oval Office.

“I think it will be very difficult for Mr. McConnell to explain how, if the public concludes that this person’s very well qualified, that the Senate should stand in the way simply for political reasons.”

Liberals vowed to pressure Senate Republicans into considering Obama’s nominee, with several groups delivering to the Senate boxes of what they said contained 1.3 million signatures from citizens demanding that a confirmation process go forward after the president announces his pick.