Republican neurosurgeon Ben Carson hosted a choir singing an Eminem cover and vowed not to be "politically correct" at the event announcing his run for president in 2016. Here are those key moments and more. (AP)

Retired neurosurgeon Ben Carson, who launched his presidential bid last week, said Sunday that he would not have gone to war with Russia over its actions in Ukraine but stressed that the Obama administration has, nonetheless, bungled its response.

“No, I wouldn’t go to war over Ukraine. But I would handle Ukraine in a very different way,” he told Chris Wallace on "Fox News Sunday." “It was agreed that they would be protected if something happened with aggression. Have we lived up to that? Of course we have not. And what does that say to our other allies around the world?”

Carson — who is running as a Washington outsider — is frequently accused by critics of lacking sufficient political experience to effectively lead the country. The renowned pediatric neurosurgeon sought to push back against those criticisms Sunday, stressing the management experience he acquired as a surgeon, through his national nonprofit and as a member of several corporate boards.

“I simply say that experience can come from a variety of different places…But I’ve had a lot of experience. World experience,” Carson said. “...[Y]ou know, there are some good people in the political arena, but I’m not sure that they, in many cases, understand real life.”

Ben Carson is a renowned pediatric neurosurgeon and Republican contender for the White House in 2016. Here's his take on Obamacare, homosexuality and more, in his own words. (Julie Percha/The Washington Post)

He also defended his economic plan, which trumpets a flat tax  — an idea that he says he got from the Bible and is "pretty darn fair."

“I got that idea, quite frankly, from the Bible. Tithing. You make 10 billion a year, you pay a billion. You make 10 dollars a year, you pay one. You get the same rights. That's pretty darn fair, if you ask me,” he told Wallace. “Some people say it's not fair because the poor people can't afford to pay that dollar. That's very condescending. I grew up very poor, I've experienced every economic level. And I can tell you that poor people have pride, too, and they don't just want to be taken care of.”

Wallace pushed back on the plan, suggesting that the numbers Carson was presenting were incorrect and that the plan favored the rich. "Let's have a battle of the experts," Carson responded.

Carson also stood by several controversial remarks he has made in the past — including comparisons between the contemporary United States and Nazi Germany — stressing that "we need to be willing to stand up and speak up for what we believe."

"There are a lot of people in our society who are afraid to say what they really mean because they may get an IRS audit, people will call them names, their jobs may be interfered with. This is not what America was supposed to be,” Carson said.

Wallace also asked Carson to clarify comments he made last week about the president’s obligation to carry out laws passed by Congress. In his comments, Carson had also stressed that the principle of judicial review, a guiding principle in the American political system, should be reconsidered.

“The way our Constitution is set up, the president or the executive branch is obligated to carry out the laws of the land. The laws of the land, according to our Constitution, are provided by the legislative branch. The laws of the land are not provided by the judiciary branch,” he told Wallace. "[T]his is an area we need to discuss. We need to get into a discussion of this because it has changed from the original intent. It is an open question."