WASHINGTON -- News of Supreme Court JusticeAntonin Scalia's death broke Saturday just hours before the GOP candidates were set to debate in South Carolina, shaking up the presidential race and immediately becoming a major election issue.

If a liberal replaces Scalia, it will likely be the biggest ideological swing in the court since Clarence Thomas replaced Thurgood Marshall -- and the first time since the 1960s, when Richard Nixon had two early appointments, that the court had a clear liberal majority.

In theory, with the conservative justice's passing, PresidentBarack Obama could nominate a replacement and the court could be majority liberal. But conservatives were alreadycalling for Senate Republicans to block any nominee until Obama is out of office.

Senate Majority Leader Mitch McConnell (R-Ky.) also made clear that he wasn't going to go along with an Obama pick. "This vacancy should not be filleduntil we have a new president," he said.

In other words, the 2016 election just got that much hotter and more intense.

Even before Scalia's death, it was clear that Obama's successor would have a hand inshaping the makeup of the bench. Many of its most consequential cases are decided on a 5-4 basis, divided between the liberal and conservative wings -- with Justice Anthony Kennedy, who turns 80 in July, the deciding vote. Political observers have long speculated on potential retirements and the likelihood that the Supreme Court's ideological bent would shift.

And on the campaign trail, the presidential candidates often speak what type of nominee they would choose if there is a vacancy, and what a high-stakes decision that would be.

“We are one justice away from the Supreme Court concluding that nobody in this room and no American has an individual right tokeep and bear arms," Sen. Ted Cruz (R-Texas) said in January, warning what would happen if liberals make up a majority. "We are one justice away from the Supreme Court striking down every restriction on abortion, and mandating unlimited abortion on demand, up until the time of birth, partial birth, with taxpayer funding, and no parental notification whatsoever."

Former Florida Gov. Jeb Bush (R), another presidential candidate, has said he would not repeat the mistake of his father, former President George H.W. Bush, who picked David Souter for the court. Souter was supposed to be a conservative choice but often ended up voting with the liberal justices.

"These picks are so important for the future of our country that if the next president gets to pick a Supreme Court justice they should pick someone -- I would pick someone -- with a proven judicial philosophybased on rulings and fight," he said in October.

Donald Trump has said he wants justices who are "smart, conservative and ... truly in love with the constitution."

Sen. Marco Rubio (R-Fla.) weighed in on Saturday and said the "next president must nominate a justice who will continue Justice Scalia's unwavering belief in the founding principles that we hold dear."

On the Democratic side, Sen.Bernie Sanders (I-Vt.) often tells crowds that he would choose a nominee who is committed tooverturning Citizens United. Former Secretary of State Hillary Clinton said in a town hall forum this month that she wants justices who are "rooted in the real world, who know that part of the genius of our system, both economic and government, is this balance of power," to ensure that it doesn't get "too far out of whack, so that business has too much power, any branch of the government has too much power."

"You know one of the many reasons why we can’t turn the White House over to theRepublicans again is because of the Supreme Court," she added.

The presidential election isn't the only important contest. Right now,Republicans control the Senate, which is why they can threaten to hold up the president's nominee. ButDemocrats have a real chance at taking back the Senate in the 2016 elections, in which case they could help a Democratic president get nominations through -- or block a GOP president from doing so.

The death of a sitting Supreme Court justice is extremely rare. Since Justice Robert Jackson died in 1954, only Chief Justice William Rehnquist passed away while still serving on the bench. Rehnquist, who was a Republican nominee, passed away during President George W. Bush's administration, so the makeup of the court did not change.

Senate Democrats are already calling on their GOP colleagues to allow an Obama nominee to go through.

"The President can and should send the Senate a nominee right away. With so many important issues pending before the Supreme Court, the Senate has a responsibility to fill vacancies as soon as possible," Senate Minority Leader Harry Reid (D-Nev.) said. "It would be unprecedented in recent history for the Supreme Court to go a year with a vacant seat. Failing to fill this vacancy would be a shameful abdication of one of the Senate's most essential Constitutional responsibilities."

According to the Congressional Research Service, since the Ford administration, it has taken the Senate an average of2.2 months for Supreme Court nominees to get a floor vote after they're nominated.

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