Former Vice President Joe Biden said Thursday he agreed with a former top military official’s view that the United States and North Korea are closer than ever to nuclear war.

Biden said in an interview with PBS NewsHour’s Judy Woodruff that he agreed with former chairman of the Joint Chiefs of Staff Mike Mullen’s comment Sunday on ABC’s “This Week” that the U.S. is “closer… to a nuclear war with North Korea” than at any previous point in history.

“Yeah, I do,” Biden said, adding he worried that the Trump administration was making “fundamental miscalculations” in its foreign policy with North Korea and other nations.

“This is not a business deal. This is not who builds the next skyscraper,” Biden said, referring to President Donald Trump’s past career as a real estate developer.

The comments came as Biden returns to the spotlight following the publication of his newest book, “Promise Me, Dad: A Year of Hope, Hardship, and Purpose.”

The book chronicles how Biden dealt with the death of his son, Beau Biden, the end of his term as vice president, and his decision not to run for president in 2016.

Biden acknowledged that Trump inherited a complex problem in dealing with North Korea. The regime launched several missile tests last year, defying international efforts to convince North Korean dictator Kim Jong-un to end the country’s nuclear weapons program.

But Biden criticized Trump’s approach, including the president’s tweet Tuesday that the United States’ “Nuclear Button” is “much bigger & more powerful” than North Korea’s.

The former vice president argued that the United States couldn’t solve the crisis alone without help from other countries.

“It can’t be done,” Biden said, “in a way that doesn’t have all the players in the game on the same page.”

Biden also touched on the ongoing demonstrations in Iran, and pushed back against criticism that the Obama administration did not support the Iranian protests following the country’s 2009 presidential election.

“He’s totally discredited the secretary of state,” Biden said, while at the same time giving “comfort to autocrats” around the world. “It has profound consequences.”

Vice President Mike Pence tweeted Monday that the U.S. would not “repeat the shameful mistake of our past” by ignoring Iranians protesting the country’s ruling regime — an apparent dig at America’s position on the Green Revolution protests in 2009.

“We did support the protesters during the Green Revolution,” Biden said, adding that the two protest movements were different and any side-by-side comparison was unfair.

Biden also defended the Iran nuclear deal reached with the U.S. and other nations in 2015, which lifted economic sanctions on Iran in return for a reduction in the country’s nuclear weapons program.

Trump promised to withdraw the U.S. from the deal as a candidate. He hasn’t done so yet as president, though speculation has increased in recent days that the latest protests could spark Trump to de-certify the deal.

“We know the regime is dangerous” Biden said of Iran, but “imagine what it would be if it had nuclear weapons right now?”

Biden argued that if the U.S. pulled out of the deal, it would isolate the country from its allies abroad and potentially put Iran in position to speed up its nuclear weapons program.

He also said that Trump’s friction with Secretary of State Rex Tillerson made it harder for the U.S. to engage with Iran and other countries. “He’s totally discredited the secretary of state,” Biden said, while at the same time giving “comfort to autocrats” around the world. “It has profound consequences.”

While Biden singled out Trump’s dealings with North Korea and Iran, he was also critical of the president’s overall leadership style.

Trump’s approach to the presidency “erodes those invisible elements of citizenship that sort of are the buoyancy for what makes this nation so special,” Biden said, adding: “It’s less his policies than the way he conducts [himself], how unpresidential he is.”

But when asked if Trump was unfit to president, Biden demurred. “The American people decided that he should be president, therefore he’s president,” Biden said. “But I think he so undermines the office, the credibility of the office and our place in the world.”