President Barack Obama has announced Susan E. Rice as his new national security adviser and Samantha Power as the pick to replace her as U.S. ambassador to the United Nations.

Rice will replace Tom Donilon, who will step down in early July. During a Rose Garden ceremony Wednesday afternoon, Obama praised Donilon’s work ethic and his “rare combination of the strategic and tactical” while helping to shape all of his foreign policy initiatives.

Obama described Rice as the “consummate public servant” and said he was “absolutely thrilled that she’ll be back at my side leading my national security team during my second term.”

Rice withdrew from consideration for the secretary of State post last year amid criticism for talking points she had delivered on the Benghazi, Libya, terrorist attack. Speculation immediately turned to her as a candidate for Donilon’s post, which does not require Senate confirmation.

Power’s nomination will require Senate confirmation, and Obama said “I’m fully confident she’ll be ready on day one,” noting her work with Rice on issues before the United Nations.

GOP Sen. John McCain of Arizona, who sits on the Foreign Relations Committee, quickly came out in favor of Power’s confirmation.

“I believe she is well-qualified for this important position and hope the Senate will move forward on her nomination as soon as possible,” he said in a written statement.

Power was a longtime Obama adviser on foreign policy before taking a break from the administration earlier this year to spend more time with her young children. She is the Pulitzer Prize winning author of “A Problem from Hell: America and the Age of Genocide.”

She and Rice strongly backed the president’s intervention in Libya, and their promotions come as the administration continues to struggle to find a coherent policy on Syria that will lead to Obama’s stated goal of ending Bashar al-Assad’s bloody reign.

Rice, in particular, has come under withering criticism from Republicans over the Benghazi talking points, despite an email document dump from the White House showing she had no role in their evolution.

“Ambassador Susan Rice deserves a subpoena from the Congress, not an apology,” Sen. Lindsey Graham, R-S.C., tweeted out last month after White House officials suggested she was owed an apology.

But other Republicans were more magnanimous in the wake of Obama’s announcement.

“I had a very good conversation with Ambassador Susan Rice to let her know I look forward to working with her on shaping important foreign policy and national security issues as she serves in her new role,” Bob Corker of Tennessee, the ranking Republican on the Senate Foreign Relations Committee, said in a written statement.