House Minority Leader Nancy Pelosi says that “it’s a good idea for the president to consider a Republican” when thinking about who to appoint to the Supreme Court. Senate Minority Leader Harry Reid on Wednesday publicly backed Nevada Gov. Brian Sandoval (R) for the job. (AP Photo/Manuel Balce Ceneta)

While Senate Republicans have quickly united in opposition to filling the Supreme Court vacancy before the November elections, President Obama faces a more complex calculation in determining what might be the best way to break that blockade.

The dilemma was thrown into stark relief Wednesday with news that Obama had been considering appointing a moderate Republican, Nevada Gov. Brian Sandoval, to fill the job left open by the late Justice Antonin Scalia: Should Democrats unite behind a moderate candidate — even a Republican who holds views anathema to the party’s base — if that is the only person who could conceivably win confirmation? Or, should Obama concede that the Senate will not confirm his pick, instead selecting a nominee who will drive voters to the polls in November to elect a Democratic president and Senate?

“The president has got some choices,” said Sen. Dianne Feinstein (D-Calif.), a senior member of the Judiciary Committee that is charged with approving a Supreme Court pick. “This has to be a special nominee to get the votes. Otherwise, it’s a useless cause.”

[Sandoval bows out of consideration for Supreme Court]

Party leaders so far are giving Obama a wide berth to make his choice. At a Thursday news conference, before Sandoval announced he was taking himself out of the running, House Minority Leader Nancy Pelosi (D-Calif.) would not criticize his potential nomination.

“I think it’s a good idea for the president to consider a Republican,” she said, quickly adding: “Or a Democrat.”

The White House is said to be considering Gov. Brian Sandoval (R-Nev.) as a nominee to replace Justice Antonin Scalia on the Supreme Court. Here's what you need to know about him. (Sarah Parnass/The Washington Post)

Senate Minority Leader Harry M. Reid, who met with Sandoval this week to discuss a potential nomination, told The Washington Post Wednesday that he would support the second-term governor if he was nominated but “would rather we had somebody a little more progressive.”

“I’ll do what I can, but I’m not pushing his name,” Reid said.

The prospect of a revolt on the party’s left flank — coming amid a presidential campaign where former Secretary of State Hillary Clinton is being pilloried by Sen. Bernie Sanders (I-Vt.) for being insufficiently liberal — would pose a real threat to any White House strategy to get a moderate confirmed.

Liberal activists are already moving to prevent a compromise nominee. One group, the Progressive Change Campaign Committee, said in a statement that any Democratic president “should appoint a nominee with a proven record in support of workers, women, minorities, and democracy issues — not someone with an unproven record or with a record provably tilted against workers and working families like Sandoval.”

The Brady Campaign to Prevent Gun Violence on Thursday declared Sandoval “unfit” for the high court, citing his 2013 decision as governor to veto legislation expanding background checks for firearm buyers in the wake of the Sandy Hook tragedy.

“Gov. Sandoval blatantly chose to abdicate the responsibilities of his position to instead comply with the demands and agenda of the corporate gun lobby,” said Dan Gross, the group’s president. “The vacancy on the Supreme Court must be filled in a timely manner, but with someone beholden to the rule of law and the American people — not the influence of special interest groups.”

Fourteen Republicans would have to break with their party to ensure confirmation if all 46 members of the Democratic conference held together. A GOP defection of that size is a tall order, and any Democratic defections would make one even more unlikely.

“Obviously, it is going to have to be somebody that the Democratic Senate feels good about,” Sen. Tim Kaine (D-Va.) said Thursday of any potential nominee.

Sen. Patrick J. Leahy (D-Vt.), the ranking member of the Senate Judiciary Committee and a veteran of more than a dozen Supreme Court nomination battles, urged his fellow Democrats not to give up on trying to push a nominee through the blockade.

“My recommendation to the president would be not to have a symbolic nominee,” he said in an interview.

The ideal nominee, he said, is “somebody Americans can look at and say, ‘Okay, I’ll trust that person with my constitutional rights.'” Asked if a Republican could pass muster, he said, “Everybody’s on the table.”

Other liberal groups are waging a public pressure campaign to get Senate Republicans to reverse course and consider a nomination but have not weighed in on what type of nominee Obama should pick.

Credo, Moveon.org, EMILY’s List and the Leadership Conference on Civil and Human Rights are already mounting petition drives and engaged in social media campaigns aimed at moderate Republican senators to stop the blockade. Targets include Sens. Pat Toomey (Pa.), Kelly Ayotte (N.H.), and Rob Portman (Ohio).

Marge Baker, executive vice president of People for the American Way, said it would be a mistake for Obama to choose a nominee he would not otherwise select just to evade the GOP blockade.

“You have to do what you think is right, and then you go forward,” she said. “It’s not a chess game.”

So far, Democrats are focused on trying to shame Republicans into taking up any nominee, regardless of their party or ideology. Pelosi, for instance, cited the GOP’s “breathtaking refusal to meet their constitutional duty” on Thursday, and Democratic senators rallied in front of the Supreme Court on Thursday to repeat their refrain of “do your job” at Republicans.

Sen. Chris Murphy (D-Conn.) said Democrats are confident that Republicans will ultimately cave: “I am struggling to find a thread of political advantage to what Republicans are doing outside of their extreme base. I think this is going to be an epic political disaster for the Republicans that will mount, week by week, month by month.”

But a few voices are calling for Obama to nominate a moderate and make a genuine attempt at getting his nominee past the Republican Senate.

Sen. Chris Coons (D-Del.), a Judiciary Committee member, said Tuesday he has told White House advisers to avoid an ideological showdown.

Nominating a “liberal Scalia,” he said, would could result in deadlock and leave the seat vacant for many, many months to come. “I don’t think this moment calls for that,” Coons said at a press briefing.

Kaine said Thursday he favored the notion of nominating a person with a “history of gaining Republican support in some way.”

“It really then poses the issue so starkly to this majority,” he said. “What is justice if not giving somebody individual consideration? Are you really going to say, ‘We don’t care at all’?”

Catherine Ho and Paul Kane contributed to this report.