Watch: Obama Rejects GOP Demands, Pledges to Appoint Scalia's Replacement

"There will be plenty of time for me to do so and for the Senate to fulfill its responsibility."

Defying demands from leading Republicans, President Barack Obama pledged Saturday evening to nominate a Supreme Court justice to fill the seat left vacant by the death of Justice Antonin Scalia.

Calling Scalia a "larger than life presence on the bench" and "one of the most consequential judges and thinkers to serve on the Supreme Court," Obama told the nation that "today is a time to remember Justice Scalia's legacy."

"I plan to fulfill my constitutional responsibilities to nominate a successor in due time," added Obama. "There will be plenty of time for me to do so and for the Senate to fulfill its responsibility to give that person a fair hearing and a timely vote. These are responsibilities that I take seriously, as should everyone. They're bigger than any one party. They are about our democracy. They're about the institution to which Justice Scalia dedicated his professional life, and making sure it continues to function as the beacon of justice that our founders envisioned."

Obama's comments were a thinly veiled rejection of calls by conservative activists and GOP politicians—including presidential candidates Ted Cruz and Marco Rubio and Senate Majority Leader Mitch McConnnell (Ky.)—to leave Scalia's seat vacant until a new president takes office next year.