What's less clear: how the spate of endangered Republicans in McConnell's caucus will react if the Kentucky Republican prevents a confirmation vote from coming to the Senate floor.
As Obama gears up for a contentious confirmation battle in the final year of his presidency, the handful of endangered Senate Republicans in swing states will become the target of intense pressure to buck their party's leadership and call for a confirmation vote, according to Democrats involved with the planning.
Privately, senior Democratic officials tell CNN there's little chance of Obama's nominee winning confirmation unless these swing-state Republicans break ranks. And on Sunday, several vulnerable incumbents, including Pat Toomey of Pennsylvania and Mark Kirk of Illinois, would not say if they wanted the Senate to deny Obama's nominee a vote.
But Republicans close to McConnell believe waiting until the next administration will be a political gift for Senate Republicans in close races. They say that if the GOP looks like it won't win the White House, GOP senators can rally conservative voters to keep their majority by claiming a Republican-led chamber will be a firewall against a liberal justice.
"I strongly agree that the American people should decide the future direction of the Supreme Court by their votes for president and the majority party in the U.S. Senate," Sen. Ron Johnson of Wisconsin, a vulnerable incumbent, said in an email to CNN.
And in a statement, Sen. Kelly Ayotte, a New Hampshire Republican facing a competitive reelection fight in 2016, said the Senate should not confirm a Supreme Court nominee until a new president is elected.
"We're in the midst of a consequential presidential election year, and Americans deserve an opportunity to weigh in given the significant implications this nomination could have for the Supreme Court and our country for decades to come," Ayotte said. "I believe the Senate should not move forward with the confirmation process until the American people have spoken by electing a new president."
The political calculation underscores the high-stakes nature of the 2016 campaign. The race for control of the Senate -- and the future of the Supreme Court -- is playing out against the backdrop of an already tumultuous presidential race. With 24 GOP Senate seats at play compared to 10 for the Democrats, both sides are already calculating how the Supreme Court vacancy could upend the high-stakes battle for the Senate, where Republicans currently hold a 54-46 majority.
Democrats believe McConnell must feel his grip on the Senate majority is at risk to let Obama's nominee come forward.
On Sunday, Sen. Chuck Schumer, the likely next Democratic leader, foreshadowed the Democratic attack line.
"The American people don't like obstruction," Schumer, a New York Democrat, said on ABC's "This Week." "When you go right off the bat and say, 'I don't care who he nominates, I am going to oppose him,' that's not going to fly."
Schumer added: "I believe that many of the mainstream Republicans, when the president nominates a mainstream nominee, will not want to follow Mitch McConnell over the cliff."
Schumer and his aides declined to comment further, but other Democratic senators and aides believe the pressure will be unsustainable, especially if the Supreme Court reaches a spate of 4-4 rulings and Obama chooses a qualified nominee widely viewed in the mainstream of judicial thought. Since 1975, no nominee has waited for a confirmation vote longer than 108 days from the time he or she was selected.
"If the Republican leadership refuses to even hold a hearing, I think that is going to guarantee they're going to lose control of the Senate," Vermont Sen. Patrick Leahy, ranking Democrat on the Senate Judiciary Committee, said Sunday on CNN's "State of the Union."
Shortly after news of Scalia's death, McConnell issued a statement eulogizing the conservative justice -- and sent a warning to the president.
"The American people should have a voice in the selection of their next Supreme Court justice," McConnell said. "Therefore, this vacancy should not be filled until we have a new president."
Moments later, Obama promised that he would still choose someone to replace Scalia, but it remains uncertain who the president will nominate or when the nomination might be announced.
McConnell's statement stopped short of saying that he would prevent a confirmation vote from even occurring. McConnell spokesman Don Stewart said the GOP leader "would have more to say" when the president submits his pick.
Two sources close to the GOP leader do not believe that McConnell would allow a vote under any circumstances, arguing that the Republicans will be able to push back against political pressure from the left by saying that the choice should be left to voters -- not members of Congress -- and that a Supreme Court confirmation fight in the president's final year in office typically does not happen.
Iowa Sen. Chuck Grassley, the chairman of the Senate Judiciary Committee, made a similar statement, saying 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."
Beth Levine, a Grassley spokeswoman, declined to comment beyond the statement, which did not address whether the Senate Judiciary Committee would have a hearing on the next nominee.
Vulnerable Republicans stay mum
Whether vulnerable Republicans will change that dynamic remains to be seen. Sen. Rob Portman of Ohio, who is in a tough Senate race, issued a statement Saturday praising Scalia's tenure on the court, but didn't address whether he opposes any nominee coming for a vote. He issued another statement Monday backing McConnell's strategy.
Toomey of Pennsylvania made similar remarks, and a spokesman declined to comment Sunday. A spokeswoman for Kirk, the Illinois Republican, didn't respond to an inquiry seeking comment.
No matter what happens in the Senate races, however, it would require a widely acceptable Supreme Court nominee in order for Obama to win confirmation. That's because he'll need at least 14 Republicans to break ranks and overcome an almost-certain filibuster, which Ted Cruz promised Sunday to wage.
"Absolutely," Cruz said when asked on ABC's "This Week" if he would filibuster any nominee. "This should be a decision for the people."
The matter is causing a clear partisan split. Sen. Joe Manchin, a centrist Democrat from West Virginia, who often votes with Republicans, wants the Senate to act on a nominee when president puts one forward, an aide to the senator tells CNN.