EXCLUSIVE: 'Not Much of an Expert' -- Obama Slaps Sarah Palin for Nuke Policy Criticism Obama is also confident the Senate will ratify new nuclear treaty.

April 8, 2010 -- In Prague to sign a nuclear disarmament treaty with Russia, President Obama pushed back against Republican critics, including Sarah Palin, who say that his new nuclear stance is too soft and leaves the United States vulnerable to attacks.

The scene Thursday at the historic Prague Castle in the capital of the Czech Republic was one of cooperation between the United States and Russia. But back home, Obama may face a challenge getting the treaty through the Senate, given Republican concerns.

Obama brushed off criticisms from former Republican vice presidential candidate Sarah Palin of his administration's recently announced nuclear policy by noting her lack of experience on the subject.

"I really have no response. Because last I checked, Sarah Palin's not much of an expert on nuclear issues," he said in an exclusive interview with ABC News' George Stephanopoulos.

Earlier this week, ahead of today's treaty signing, Obama announced plans to end the development of new nuclear weapons in the U.S. and impose a new policy, not included in the new treaty, that the United States will not use nuclear weapons against any country that has signed and is abiding by the Nuclear Non-Proliferation Treaty, even if they attack the United States with chemical or biological weapons.

In an appearance Wednesday on Fox News, Palin compared Obama to a kid in a playground who is asking for a punch in the face.

"It's unbelievable. Unbelievable," said Palin on Wednesday evening while appearing on Sean Hannity's Fox News program. "No administration in America's history would, I think, ever have considered such a step that we just found out President Obama is supporting today. It's kinda like getting out there on a playground, a bunch of kids, getting ready to fight, and one of the kids saying, 'Go ahead, punch me in the face and I'm not going to retaliate. Go ahead and do what you want to with me.'"

Obama told Stephanopoulos in Prague that he was not concerned about Palin's criticisms. "If the Secretary of Defense and the Chairman of the Joints Chiefs of Staff are comfortable with it, I'm probably going to take my advice from them and not from Sarah Palin," he said.

Despite signs of Republican opposition, Obama said today that he is confident that the new nuclear disarmament treaty he signed with Russian President Medvedev will be ratified by the Senate.

"When they have had the opportunity to fully evaluate this treaty, they will come to the conclusion that this is in the best interest of the United States," Obama said of Senate Republicans who have voiced concerns about the new treaty.

Obama told Stephanopoulos that the treaty is "absolutely vital" to his administration's nuclear proliferation agenda.

"I will also say to those in the Senate who have questions is that this is absolutely vital for us to deal with the broader issues of nuclear proliferation, that are probably the number one threat that we face in the future," the president said.

Obama sat down with Stephanopoulos at Prague Castle after signing the historic new nuclear disarmament treaty with Russia President Medvedev.

Obama and Medvedev pledged today to reduce their nation's nuclear stockpiles by a third, from 2,200 deployed warheads for each country to 1,550 over seven years. The treaty signing comes after more than a year of intense negotiations and several missed deadlines between the United States and Russia.

The scene in Prague was one of cooperation between the United States and Russia but back home, the Obama administration may face a challenge getting this treaty through the Senate.

The agreement requires the support of two-thirds of the Senate (67 votes) for ratification. Given the Democrat's 59-seat majority, it looks as if they will need at least eight Republicans to get on board to make the treaty official.

Senate Republican leadership sources say the minority's leaders don't have a firm position because they have not been consulted in any substantive way about the treaty by the Obama administration beyond some minor discussions.

This week the White House has been consistently emphasizing that past Senate votes on nuclear arms reduction treaties passed with overwhelming bipartisan support.

Obama Says U.S., Russian Differences Over Missile Defense Will Not Affect Nuclear Treaty

"If you look back at previous nuclear reduction treaties in the late '80s, the early '90s, and even as late at 2003, these are documents that enjoy vast bipartisan majorities -- votes in the '90s," White House press secretary Robert Gibbs told reporters on Air Force One en route to the Czech Republic. "We are hopeful that reducing the threat of nuclear weapons remains a priority for both parties."

Earlier today in Prague, Obama expressed confidence that the treaty would be ratified.

"I am actually quite confident that Democrats and Republicans in the United States Senate having reviewed this will see that the United States has preserved its core national security interests," he said. "That it is maintaining a safe and secure and effective nuclear deterrent but that we are beginning to once again move forward leaving Cold War behind to address new challenges in new ways."

But in the interview with ABC News' Stephanopoulos, Obama would not declare definitely that he knew how the issue would play out in the Senate.

"I've now been in Washington for long enough that for me to say I have no doubt how the Senate operates would be foolish," he said.

Obama singled out the ranking Republican on the Senate Foreign Relations Committee, Sen. Dick Lugar, R-Ind., as a Republican leader that he has confidence in based on their work together on this issue when Obama was in the Senate.

Lugar's view, which will carry some weight among his fellow Republicans, is said to be "favorable," a Lugar aide tells ABC News, but he needs to do "due diligence" and go through the process of reading the treaty and its annexes, which will take some time.

Obama told Stephanopoulos that his administration is "absolutely confident" that the new nuclear treaty will in no way impede the U.S. ability to move forward on a missile defense program.

"It is going to be contingent and developing based on our threat assessments," the president said.

White House Starts Working with Senate to Ratify Treaty

"If for example, we are able to create a situation where Iran is no longer posing us a threat in terms of intercontinental ballistic missiles, then it may be that our missile defense configuration is able to be scaled back in a way that doesn't threaten Russia," he told Stephanopoulos.

Obama said that the new disarmament treaty signed today is "only a start."

"We're looking at a timetable over a five, 10, 15, 20 year time horizon," he said. "We're going to have to continually build and evolve a whole approach that is designed for the 21st century as opposed to the 20th century."

The U.S. plans for a missile defense system still remain a key sticking point between the two nations and Medvedev warned once again that the Russians could pull out from the treaty if they felt it undermined the new foundation of arms control.

Obama disputed that notion to Stephanopoulos and said the Russians are not saying they would withdraw from the treaty over the missile defense system.

"We were firm, and are now absolutely confident that this in no way impedes our ability to move forward on the missile defense program, that's designed not to target Russia," he said in the ABC News interview.

Obama said in remarks in Prague that his administration's plans are not aimed at changing the "strategic balance" with Russia but instead were established with the goal of "protecting the American people" from missile attacks from other nations.

The White House said its work with the Senate will begin immediately and its expectation is that the Senate will sign off on the treaty this year.

"We are hopeful that reducing the threat of nuclear weapons remains a priority for both parties," Gibbs told reporters on Air Force One en route to Prague. "I think it's the president's hope and expectation the Senate will ratify this, this year."

Starting today, administration officials will begin briefing members of the Senate on the specifics of the treaty.

The Russian parliament, the Duma, also needs to sign off on the new disarmament treaty.

ABC News' Jake Tapper, Yunji de Nies and Sunlen Miller contributed to this report.