Donald Trump, in an extensive interview with Fox News’ Megyn Kelly, responded to critics of his barbed campaign style by saying he never would have been successful in the primary race if he had acted “presidential” and held back on hitting his political rivals – while declaring that if he doesn’t win the election this fall, he’ll consider his campaign a “complete waste.”

The presumptive Republican presidential nominee was blunt in describing the stakes of the 2016 race as he sees it. Without a victory in the fall, he said, he won’t be able to lower taxes, strengthen the military or “make America great.”

“I will say this: If I don’t go all the way, and if I don’t win, I will consider it to be a total and complete waste of time, energy and money,” Trump said, in the interview that aired Tuesday night on Fox Broadcast Network affiliates.

The candidate addressed a range of topics in his sit-down with Kelly, from his tone to the lead-off presidential debates to his past clashes with the Fox News host.

Trump conceded that, in looking back, he “absolutely” has regrets, without going into detail. But he said if he hadn’t conducted himself in this way, he wouldn’t have come out on top.

“If I were soft, if I were presidential … in a way it’s a bad word, because there’s nothing wrong with being presidential, but if I had not fought back in the way I fought back, I don’t think I would have been successful,” he told Kelly.

Trump argued that he’s a “counter-puncher” who’s only responding to the attacks against him.

“I respond pretty strongly, but in just about all cases, I’ve been responding to what they did to me,” Trump said. “It’s not a one-way street.”

The interview was conducted on the heels of an April meeting between Kelly and the Republican candidate at Trump Tower in New York City.

Before that meeting, the two had been at odds for months – dating back to a Fox News-hosted debate last August, when Trump accused “The Kelly File” host of asking him unfair questions.

Today, Trump is the presumptive Republican presidential nominee, having vanquished 16 primary rivals and now turning his attention toward an expected general election battle against Democratic front-runner Hillary Clinton. The former secretary of state, while still trying to shake a primary challenge from Bernie Sanders, has sharpened her criticism of Trump as well in recent weeks, even saying Monday that he’s a “loose cannon” who would be dangerous for the country. And she said he’d return to “failed” economic policies.

Speaking with Kelly, Trump suggested the August debate actually helped prepare him for the battle ahead.

“In a certain way, what you did might have been a favor, because I felt so good about having gotten through -- I said, ‘If I could get through this debate, with those questions, you can get through anything,’” he said.

Trump pointed to that debate when asked at what moment he realized he might actually win the race. “I think that first debate meant something,” Trump said, adding that he felt comfortable with the subject matter and the people he was competing against.

At the same time, Trump tried to explain why he fired back at Kelly for confronting him about his past disparaging comments about women. “I thought it was unfair,” Trump said of the question, while noting it was the first question he’d ever been asked at a debate. “And I’m saying to myself, man, what a question.”

He added, “I don’t really blame you because you’re doing your thing, but from my standpoint, I don’t have to like it.”

As for his role in the presidential election in this year, Trump said: “I really view myself now as somewhat of a messenger… This is a massive thing that’s going on. These are millions and millions of people that have been disenfranchised from this country.”

Trump for the last several weeks has been working to reach out to members of the so-called Republican establishment in Washington he’s spent much of his campaign railing against. He met last week with GOP congressional leaders, including House Speaker Paul Ryan – who has held back an endorsement for now. Trump and the lawmakers came away describing the meetings as positive.

In the interview with Kelly, Trump briefly discussed his personal life, and how his older brother Fred died after a battle with alcoholism. “I have never had a glass of alcohol,” he said, calling his brother’s death the “hardest thing for me to take.”

And while defending his tone on the campaign trail, Trump also said he takes “very seriously” the responsibility of the office he’s seeking.

“I understand what's going on. And when I see the fervor, when I see 25,000 people that have seats, and not one person during an hour speech will sit down. I say, sit down, everybody, sit down. And they don't sit down," he said. "… I mean, that's a great compliment. But I do understand the power of the message. There's no question about it.”