The billionaire businessman was unapologetic -- and as defiant as ever -- about a number of controversies that have inundated his presidential campaign in a wide-ranging interview with CNN's Anderson Cooper that aired on Wednesday and Thursday.

The brash real estate mogul and former host of the reality TV show, "The Apprentice," has come under attack for referring to some immigrants coming into the United States as "rapists." Trump also addressed head-on a Washington Post report that said there were illegal immigrants working at one of Trump's hotel construction sites in Washington. And he said he still isn't totally convinced President Barack Obama was born in this country.

Speaking at the Trump Tower in midtown Manhattan, Trump also took on his fellow presidential candidates and insisted of his long-shot White House bid: "I'm in it to win it."

Trump: I can't guarantee all my workers are legal

Trump: I can't guarantee all my workers are legal 03:54

Trump: I can't guarantee all my workers are legal

The Republican field

Trump has surged in national polls recently, but the competition he faces is fierce. In the interview, Trump did not have many kind words for his opponents in the large GOP field.

"Bush is weak on immigration. Forget about his stance on Common Core, which is a total disaster," Trump said of Jeb Bush.

Florida Sen. Marco Rubio is also "extremely weak" on immigration, Trump said, adding: "If he ever got elected, you would have people flown across the border."

He mused that South Carolina Sen. Lindsey Graham seems to want to "bomb everybody."

"All I know is that every time I watch Lindsey Graham he wants to bomb everybody. Let's bomb everybody," he said.

Trump also criticized the GOP's 2012 presidential nominee, Mitt Romney, for failing to energize the party's base.

"He didn't appeal to a lot of people. He didn't appeal to conservative Republicans," Trump said. "I said to Mitt Romney and his people, why aren't you on television the last two three weeks? Why aren't you doing television now? They were sitting around, taking it easy. He choked."

Obama's birthplace

Not that long ago, Trump was an outspoken skeptic about whether Obama was born in the United States.

Now, he insists he's not really interested in talking about the issue.

"Honestly, I don't want to get into it," Trump said. "I'm about jobs, I'm about the military, I'm about doing the right thing for this country."

But to be clear, Trump is still not totally convinced that Obama was born in the country.

"I don't know. I really don't know," he said. "I don't know why he wouldn't release his records."

In 2011, Obama released his original long-form birth certificate in response to speculation about his birthplace.

'Can't guarantee' legal status of his own workers

Trump said Wednesday that he "can't guarantee" that all of the workers he employs have legal status in the United States, and warned that if he were to discover any illegal immigrants working for him, "We would get rid of them immediately."

A recent Washington Post report that said there are illegal immigrants working at the Old Post Office Pavilion construction site in Washington, which Trump is converting into a luxury hotel.

Trump said that the buck "absolutely" stops with him and that he wished the Post article had named the alleged illegal workers so he could take prompt action.

"We have gone out of our way to make sure that everybody in that building is legal," he said. "I wish they would give us some names, we would get them out immediately."

JUST WATCHED Trump: No regrets about re-tweet Replay More Videos ... MUST WATCH Trump: No regrets about re-tweet 01:17

'Mexican' tweet about Jeb Bush's wife

Trump addressed a racially charged tweet this week that further fueled the ongoing controversy about his views on immigrants.

His account, @realDonaldTrump, retweeted the message: "#JebBush has to like the Mexican Illegals because of his wife."

According to The Wrap , which captured a screen grab of the tweet, the tweet was deleted soon after.

Trump said in the CNN interview that he had never authorized that retweet, but was nevertheless unapologetic.

"Do I regret it? No, I don't regret it," Trump said.

He said that he believed the immigration stance of fellow GOP presidential candidate and former Florida Gov. Jeb Bush may be influenced by his wife's background.

"If he loves his wife and she's from Mexico, I think it probably has an influence on him, yes. I can understand that." Trump said.

The death of Kate Steinle

An undocumented immigrant has been accused of fatally shooting a woman in San Francisco named Kate Steinle

That tragedy, in Trump's opinion, represents precisely what's wrong with the country's immigration system.

"This man, or this animal, that shot that wonderful, that beautiful woman in San Francisco, this guy was pushed back by Mexico," Trump said. "Mexico pushes back people across the border that are criminals, that are drug dealers."

As he has in the past, Trump pledged that as president, he would build an "impenetrable" wall along the country's southern border to keep out unwanted individuals.

Unfazed by corporate backlash

In the aftermath of his inflammatory comments about immigrants, corporations across the country announced that they would no longer do business with Trump.

But even as companies like Macy's, NBC and ESPN have turned their backs on Trump, the former reality TV star has remained defiant, even doubling down on his original remarks.

On Wednesday, Trump dismissed the business deals he's lost in the last few weeks, saying they've hardly put a dent in his massive wealth.

"Here's the good news. I'm very rich," Trump said. "The money you're talking about is a lot but it's peanuts for me."

Donations to Democrats

Although Trump is now seeking the Republican Party's nomination for president, he has given generously to Democrats in the past.

Trump's past beneficiaries include the Democratic National Committee, New York Sen. Kirsten Gillibrand and even Hillary Clinton , whom Trump referred to as the "worst secretary of state in the history of the United States" on Wednesday.

The businessman defended his previous donations to Democrats, chalking them up as a necessary business decision.

"As a businessman in New York City, I have to get along with Democrats," he said. "If I don't get along with Democrats, I'm sort of like, out of business."

He dismissed the accusation from some Republicans that his past financial support for those across the aisle makes him a flip-flopper.

"I get along with everybody. People love me," he said. "Everybody loves me."

JUST WATCHED Trump: I would 'bomb the hell' out of Iraqi oil fields Replay More Videos ... MUST WATCH Trump: I would 'bomb the hell' out of Iraqi oil fields 01:26

Fighting ISIS

President Trump's strategy for fighting ISIS? "Bomb the hell out of those oil fields."

Trump, who has long been openly critical of the the Obama administration's foreign policy strategy, said Wednesday that "nobody would be tougher on ISIS than Donald Trump."

The best strategy for knocking out ISIS is to take away their wealth, Trump said, by destroying oil fields in Iraq that are controlled by ISIS.

"I would bomb the hell out of those oil fields," Trump said.

He added that once the oil fields are destroyed, he would deploy big oil companies like Exxon to rebuilt them.

"They would rebuild them so fast your head will spin," he said.