On Wednesday afternoon, President Obama announced the resignation of National Security Adviser Tom Donilon, who spent more than four years at the National Security Council. Donilon will leave his post in early July and will be succeeded by Ambassador Susan Rice. The president also announced that he will nominate Samantha Power to succeed Rice as Ambassador to the U.N.

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Of Donilon, the president said the country "owes him a debt of gratitude," saying that his efforts during his time as adviser helped to restore the nation's prestige in the world.

President Obama described Rice as a "fearless" and "tough" advocate for justice who is both passionate and pragmatic.

"Susan was a trusted advisor during my first run as president," he said. "I am absolutely thrilled she'll be back at my side leading the national security team in my second term."

Read the full transcript, below:

President Barack Obama announces Susan Rice as new National Security Advisor in the White House Rose Garden.

Good afternoon. It is a beautiful day and it's good to see so many friends here. Of all the jobs in government, leading my National Security Team is probably one of the most demanding, if not the most demanding.

And so since the moment I took office, I've counted on the exceptional experience and insights of Tom Donilon. Nearly every day for the past several years, I've started every morning with Tom leading the Presidential daily briefing; hundreds of time, a sweeping assessment of global developments and the most pressing challenges.

As my National Security Advisor, his portfolio is literally the entire world. He is deftly advanced our strategic foreign policy initiatives while at the same time having to respond to unexpected crises and that happens just about every day.

He has overseen and coordinated our entire National Security team across the government; a herculean task and it's non-stop, 24/7, 365 days a year.

Today I am wistful to announce that after more than 4-years of extraordinary service, Tom has decided to step aside in the beginning of July. And I am extraordinarily proud to announce my new National Security Advisor, our outstanding Ambassador to the United Nations Susan Rice as well. [applause]

As well as my nominee to replace Susan in New York, Samantha Power. [applause]

Now when I first asked Tom to join my team, I knew I was getting one of our nation's premier foreign policy leaders, someone who had a deep sense of history and a keen understanding of our nation's place in the world.

He shared my view that in order to renew American leadership to the 21st century, we had to fundamentally rebalance our foreign policy. And more than that, he knew how we could do it. You see, Tom is that rare combination of the strategic and the tactic. He had a strategic sense of where we need to go and he has a tactical sense of how to get there.

Moreover, Tom's work ethic is legendary. He began his public service in the Carter White House when he was just 22 years old. And somehow he has been able to manage to maintain the same drive and the same stamina and the same enthusiasm and reverence for serving in government.

He's helped shaped every single national security policy of my presidency and forging a new national security strategy rooted in our economic strength here at home to ending the war in Iraq. Here at the White House, Tom oversaw the operation that lead us to Bin Laden. He's helped keep our transition on track as we wind down the war in Afghanistan.

At the same time, Tom has played a critical role as we've bolstered the enduring pillars of American power; strengthening our alliances Europe to Asia, enhancing our relationship with key powers, and moving ahead with new trade agreements and energy partnerships.

And from our tough sanctions on Iran to our unprecedented military and intelligence cooperation with Israel [inaudible audience interruption] It's true. From New Start with Russia to deeper partnerships with emerging powers like India and stronger ties with the Gulf states; Tom has been instrumental every step of the way.

I'm especially appreciative to Tom for helping us renew American leadership in the Asia-Pacific where so much of our future security and prosperity will be shaped. He's worked tirelessly to forge a constructive relationship with China that advances our interests and our values. And I'm grateful that Tom will be joining me as I meet with President Xi of China this week.

And finally, Tom, I'm personally grateful for your advice, for your counsel and most of all, for your friendship. Whenever we sit down together, whether it's in the Oval Office or the situation room, I do so knowing that you have led a rigorous process; that you've challenged assumptions; that you've asked the tough questions; that you've led an incredibly hard-working national security staff, and presented me with a range of options to advance our national interests.

A president can't for many -- anything more than that. And this is a testament to your incredible professionalism, but also your deep love of country. I know that this relentless pace has meant sacrifices for your family -- for Cathy, who is here, Dr. Biden's former chief of staff, who I was proud to nominate as our new global ambassador for women; and for Tom and Cathy's wonderful children Sarah (ph) and Teddy (ph).

So, today I want to publicly thank all the Donilons for their abiding commitment to public service that runs through the family. [APPLAUSE].

You've been with me every step of the way these past four years. The American people owe you an enormous debt of gratitude for everything you've done. You've helped to restore our nation's prestige and standing in the world. You've positioned us well. Continue to lead in the years ahead. I think that Tom Donilon has been one of the most effective national security advisors our country has ever had. And he's done so without a lot of fanfare and a lot of fuss. So Tom, on behalf of us all thank you for your extraordinary service. [APPLAUSE]

Now I am proud that this work will be carried on by another exemplary public servant Ambassador Susan Rice. [APPLAUSE] Susan was a trusted advisor during my first campaign for President. She helped to build my foreign policy team and lead our diplomacy at the United States in my first term. I am absolutely thrilled she will be back by my side leading national security team in my second term.

With her background as a scholar, Susan understands that there's no substitute for American leadership. She is at once passionate and pragmatic. I think everybody understands that Susan is a fierce champion for justice and human dignity. But she's also mindful that we have to exercise our power wisely and deliberately.

Having served on the national security council staff herself, she knows how to bring people together around a common policy and then push it through to completion so that we're making a difference where it matters most. Here in the country that we pledge to defend and in the daily lives of people we're trying to help around the world.

Having served as an assistant secretary of state, she knows our policies are stronger when we harness the views and talents of people across government. So Susan's a consummate public servant. A patriot who puts her country first. She is fearless. She is tough. She has a great tennis game and a pretty good basketball game. Her brother's here who I play with occasionally. And it runs in the family, throwing the occasional elbow. But hitting the big shot. [LAUGHTER]

As our Ambassador to the UN, Susan has been a tireless advocate in advancing our interests. She's reinvigorated American diplomacy in New York. She's helped to put in place tough sanctions on Iran and North Korea. She's defended Israel. She's stood up for innocent civilians from Libya to Cordorba. She supported an independent South Sudan. She's raised her voice for human rights including Women's rights. Put simply, Susan exemplifies the finest tradition of American diplomacy leadership.

So thank you Susan for willing to take on this next assignment. I am absolutely confident you're going to hit the ground running. And I know that after years of commuting to New York while Ian, Jake and Maris stay here in Washington, you will be the first person ever in this job who will see their family more by taking the National Security Advisor's job. [APPLAUSE]

Now normally, I'd be worried about losing such an extraordinary person up at the United States. Trying to figure out how are we ever going to replace her. But fortunately, I'm confident we've got an experienced, effective and energetic UN Ambassador in waiting in Samantha Pollard.

Samantha first came to work for me in 2005 shortly after I became a United States Senator. As one of country's leading journalists, I thinks he won the Pulitzer prize at the age of 15 or 16. One our foremost thinkers on foreign policy. She showed us that the international community has a moral responsibility and a profound interest in resolving conflicts and defending human dignity.

As a senior member of my national security team, she's been a relentless advocate for American interests and values. Building partnerships on behalf of democracy and human rights fighting the scourge of anti-Semitism and combating human trafficking. To those who care deeply about America's engagement and indispensible leadership in the world, you will find no stronger advocate for that cause than Samantha.

And over the last four years, Samantha has worked hand and glove with Susan in her role because Samantha's been the lead White House staffer on issues related to the United States. And I'm fully confident she will be ready on day one to lead our mission in New York while continuing to be an indispensible member of my national security team.

She knows the UN's strengths. She knows its weaknesses. She knows that American interests are advanced when we can rally the world to our side. And she knows that we have to stand up for the things that we believe in. And to ensure that we have the principle leadership that we need in the United States, I will strongly urge the Senate to confirm her without delay. So Samantha, thank you. To Cass and you and Decklan and Rian for continuing to serve our country.

This team of people has been extraordinarily dedicated to America. They have made America safe. They have made America's values live in corners of the world that are crying out for our support and our leadership. I could not be prouder for these three individuals. Not only their intelligence, not only their savvy, but their integrity and their heart. And I'm very very proud to have the privilege of working with Tom. Very proud that I'll continue to have the privilege of working with Samantha and with Susan. So with that I'd invite Tom to say a few words. Tom? [APPLAUSE]