Justice Deferred? The death of a Supreme Court justice and the battle over who will fill his seat--and when.

• Author: Smith, Patricia
• Position: NATIONAL - Antonin Scalia

The unexpected death of Supreme Court Justice Antonin Scalia has set off a massive political battle over who will succeed him, and it could have a huge impact on critical cases the Court is now considering.

Almost immediately after Scalia's death last month at the age of 79, Republican senators said President Obama should hold off on nominating a replacement and leave the task to whoever wins the presidential election in November.

"The American people should have a voice in the selection of their next Supreme Court justice," said Senator Mitch McConnell of Kentucky, the Republican majority leader. "Therefore, this vacancy should not be filled until we have a new president."

The president immediately countered that he wouldn't wait. "I plan to fulfill my constitutional responsibilities to nominate a successor in due time," Obama said, adding, "These are responsibilities that I take seriously, as should everyone. They are bigger than any one party, they are about our democracy."

The stakes are incredibly high. The nine-member Court has been ideologically split between conservatives and liberals, with one justice often providing a "swing vote" to tip a ruling one way or the other (see "A Court in Transition"). Scalia was for decades the Court's most outspoken and influential conservative, so replacing him with a liberal--or even a moderate--justice would have a profound impact. President Obama's two previous Supreme Court appointees, Sonia Sotomayor and Elena Kagan, both replaced liberal-leaning justices, so their appointments didn't change the overall makeup of the Court.

If Obama succeeds in replacing Scalia, he would be the first president since Ronald Reagan to fill three seats on the court. To be confirmed, a Supreme Court nominee needs a simple majority of votes in the Senate. With 54 seats in the 100-member Senate, Republicans have the power to block the confirmation--if they all vote against Obama's nominee.

The vacancy has already become a huge issue in the election, with Republican candidates supporting McConnell's view that such an important vacancy shouldn't be filled during a presidential election year, and Democrats accusing Republicans of plotting to circumvent the Constitution.

"Justice Scalia was an American hero," Republican candidate Ted Cruz tweeted. "We owe it to him, & the Nation, for the Senate to ensure that the next President names his replacement."

Democrat Hillary Clinton countered in her own tweet: "I have news for...