“Millions of people are just months away from determining the senators who should vote to confirm or reject the president’s nominee and their voices deserve to be heard now as Leader McConnell thought they deserved to be heard then. Anything but that would be the absolute height of hypocrisy,” Schumer said.
In a letter addressed to President Donald Trump, Kennedy said he intended to end his time as an associate Justice starting July 31.
"For a member of the legal profession it is the highest of honors to serve on this Court," Kennedy wrote. "Please permit me by this letter to express my profound gratitude for having had the privilege to seek in each case how best to know, interpret, and defend the Constitution and the laws that must always conform to its mandates and promises."
Trump told reporters Wednesday that officials will immediately begin the search for a new Supreme Court Justice. The president said he plans to chose from the list of 25 people he previously considered to fill late Justice Antonin Scalia’s seat.
“He is a man who has displayed tremendous vision and tremendous heart, and he will be missed,” Trump said. “Hopefully we’ll pick someone who will be as outstanding.”
Senate Majority Leader Mitch McConnell said Wednesday that lawmakers will vote this fall to approve of Kennedy’s replacement.
Kennedy, 81, was appointed to serve on the nation’s highest court in 1987 by President Ronald Reagan. He took his oath of office on Feb. 18, 1988.
“It has been the greatest honor and privilege to serve our nation in the federal judiciary for 43 years, 30 of those years on the Supreme Court,” Kennedy said in a statement released by the Supreme Court. He added that he made his decision to leave in order to spend more time with his family.
He is the longest-serving Justice currently on the court.
Kennedy has been considered the “swing” vote among the nine justices for many years. With four strong conservatives -- Samuel Alito, Clarence Thomas, John Roberts and the late Scalia -- and four equally strident liberals -- Elena Kagan, Sonia Sotomayor, Stephen Breyer, Ruth Bader Ginsburg -- it often fell to the moderate Kennedy to cast a deciding vote on a case.
His decision leaves the court split with four liberal justices who were appointed by Democratic presidents and four conservatives chosen by Republicans. It also gives Trump the chance to cement conservative control of the high court.
Trump’s first high court nominee, Justice Neil Gorsuch, was confirmed in April 2017.
The Associated Press contributed to this report.