Sen. Charles E. Grassley (R-Iowa), shown in Des Moines on Feb. 1, could find himself at the center of the nomination process in the search to find Antonin Scalia’s successor on the Supreme Court. (Andrew Harrer/Bloomberg News)

As the White House shifts its vetting of potential Supreme Court nominees into high gear, the handling of that nomination is set to rest largely with the 82-year-old chairman of the Senate Judiciary Committee, Sen. Charles E. Grassley.

Grassley (R-Iowa) said in a Washington Post op-ed published Friday, co-authored with Senate Majority Leader Mitch McConnell (R-Ky.), that the Senate should “withhold its consent” for anyone President Obama nominates to succeed the late Justice Antonin Scalia.

But in earlier public comments, Grassley did not rule out holding hearings or votes on the nominee — which have emerged as points of division for Senate Republicans determined to block an Obama nominee but also blunt political attacks that could threaten their majority in November.

“Take it a step at a time,” Grassley told Iowa reporters on Tuesday.

Grassley’s steps as Judiciary chairman stand to put the plainspoken farmer at the center of a months-long, bare-knuckle political fight unlike any other he has experienced during his 35 years in the Senate.

White House press secretary Josh Earnest said Friday that it will probably be a few weeks before Obama makes a nomination. The list of candidates is not yet final, he said, but lawyers have prepared dossiers on potential nominees’ records, professional experience and other matters, “and I suspect the president will be dedicating a significant portion of his weekend digging into that information.”

Friday evening, Obama walked from the West Wing to the residence holding a binder filled with briefing material on potential nominees. Asked by reporters to offer up some names, the president demurred.

Grassley is among a group of key Senate leaders, including McConnell, Minority Leader Harry Reid (D-Nev.) and ranking Judiciary Committee Democrat Patrick J. Leahy (D-Vt.), whom Obama has called to convey his determination to make a nomination.

Last year, Grassley became the first non-lawyer ever to chair the Judiciary Committee, passing up opportunities to helm the powerful Finance or Budget panels for a chance to oversee judicial confirmations and influence many other legal matters.

Grassley made numerous, sometimes contradictory Supreme Court-related comments earlier this week, but he did not make any public statements Friday after the publication of the op-ed. Grassley spokeswoman Beth Levine said the senator is not likely to address the matter over the weekend. Republican senators are expected to meet behind closed doors to plan a path forward once they return to Washington on Tuesday.

Grassley has vowed to block any Obama nomination, beginning hours after Scalia’s death was announced last Saturday, when he declared that “it only makes sense that we defer to the American people who will elect a new president to select the next Supreme Court justice.”

But after spending his entire Senate career on the Judiciary Committee and participating in confirmation hearings for 13 Supreme Court nominees, the senator might find it difficult to pass up the chance to chair one himself. He is also seeking election to a seventh term this year, and while he has not attracted serious competition, he may wish to avoid becoming a symbol of Washington obstruction.

Criticism has been directed at Grassley from both directions. The editorial page of Iowa’s largest newspaper, the Des Moines Register, said this week that he was wrong to “disregard his constitutional duty by rejecting a nominee who hasn’t even been named.”

Conservatives, meanwhile, are skeptical of Grassley’s decision to move criminal justice reform legislation and his willingness to advance a handful of Obama’s lower-court nominees. Any move to consider a Supreme Court nominee, activists say, would infuriate the Republican base.

“Holding a hearing would suggest that there is some reason the American people should in fact be robbed of this unique opportunity to weigh in on the next president and thus the next justice,” said Dan Holler of Heritage Action for America, an advocacy group that called last month for a total shutdown of judicial confirmations.

In a Dallas talk-radio interview Wednesday, Senate Majority Whip John Cornyn (R-Tex.) sought to tamp down conservative fears: “Nobody can roll Chuck Grassley, and I predict that he will stand firm on this.”

As the debate over Scalia’s replacement raged on, the president and first lady went to the Supreme Court on Friday afternoon to pay their respects as his body lay in repose in the Great Hall. The two met “privately with some members of Justice Scalia’s family,” Earnest said later.

Some conservatives have criticized the president for not attending Saturday’s funeral Mass for Scalia, but Earnest said Friday’s visit gave Obama an opportunity “to both pay his personal respects to those who loved Justice Scalia, but also pay tribute to the outsized impact that he had on the country and on our legal system.”

Obama’s initial outreach to Senate leaders came just as Vice President Biden said in interviews Thursday evening that Obama needs to pick a consensus candidate to win Senate approval. “The idea that we’re going to go in and decide we’re going to pick an, I don’t know, a new Justice [William J. Brennan Jr.], I don’t think that’s going to happen. That’s not how the system works,” he said.

Earnest would not comment Friday on whether the president feels compelled to pick a moderate, but acknowledged that “the president’s nominee will need bipartisan support.” He also did not rule out the idea of Obama selecting a high-ranking administration official, such as Attorney General Loretta E. Lynch.