On February 13, 2016, Associate Justice of the Supreme Court, Antonin Scalia, died of natural causes, he was 79 and had suffered from heart problems.
The Supreme Court, which is the highest court in the United States, is made up of nine judges in order to avoid ties over major decisions. If a court case is particularly important or controversial (like the Dred Scott v Sandford, Plessy v. Ferguson, Roe v. Wade etc.), it is decided here and then the decision remains in place until a historical event or new court decision changes its status.
For example, the 1857 Dred Scott decision which deemed that African-Americans were not citizens and that slaves were property was overturned after the U.S. Civil War and subsequent 13th and 14th amendments. Plessy v. Ferguson in 1896, which ruled that "separate but equal" facilities for black and white Americans was not unconstitutional, was overturned in 1954 by the Brown v. Board of Education decision. Roe v. Wade legalized abortion in 1973 and, more recently, the Supreme Court legalized gay marriage in 2015. Supreme Court decisions, therefore, can determine laws and cultural norms for generations.
Antonin Scalia was a conservative judge who voted against gay marriage (despite his vote, five out of the nine justices voted to legalize the practice) and made some controversial comments like the one below.
"There are those who contend that it does not benefit African-Americans to get them into the University of Texas, where they do not do well, as opposed to having them go to a less-advanced school, a slower-track school where they do well." (Quoted from Antonin Scalia)
Scalia's death really complicates the election process this year since the appointment of a new judge may end up going to the new president - here's why:
Barack Obama, as president, has the constitutional right and duty to appoint judges who will then serve for life (or at least until they choose to retire) but the Republican congress has vowed to do whatever they can to draw out the process by rejecting his appointments - thereby pushing the decision to America's next president.
That means if Ted Cruz becomes president, he will appoint a very conservative judge who will tilt the balance in the court towards conservativism (no more abortion rights, re-introducing prayer in school, loss of immigrant rights etc.). If Bernie Sanders wins, his selection could be very liberal (fewer rights for the wealthy, more rights to the poor, restrictions on gun rights etc.). Since the judge is elected for life, this decision will affect America for decades.
Right now there are four conservative judges and four liberal judges - an even split -- and there are a number of cases that are already scheduled to be heard in the Supreme Court on contraception, abortion, immigration, and voting rights. If there is a tie, then the case may go back to the lower court or be postponed until a new supreme court judge is appointed.
The current makeup of the Supreme Court:
Four liberals: Kagan (appointed by Obama), Sotomayor (Obama), Breyer (Clinton), Ginsberg (Clinton)
Four Conservatives: Roberts, (G. W Bush), Alito (G.W. Bush), Thomas, (G.H. Bush), Kennedy (Reagan)