Former Vice President Joe Biden said he believes that President Donald Trump was right to walk away from the second summit with North Korea.

"The president did the right thing by walking away," Biden said while visiting the University of Nebraska at Omaha on Thursday.

However, the potential 2020 candidate also slammed the president on his approach to diplomacy.

"But diplomacy matters; preparation matters," he continued. "The president treats everything like it's a real-estate deal."

Former Vice President Joe Biden said that President Donald Trump was right to walk away from the second summit with North Korea. However, the potential 2020 candidate had sharp words for the president's brand of diplomacy.

Biden was speaking at the first Chuck Hagel Forum in Global Leadership at the University of Nebraska in Omaha, Nebraska on Thursday. He was in conversation with Hagel, who is not only a former Republican senator, but also served as US secretary of defense during the Obama administration.

The two former, longtime Senate colleagues discussed the role of US leadership in global affairs.

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"American leadership and engagement in the world is essential," Biden said, according to the Lincoln Journal Star. "If the US fails to lead, who will take our place?"

Biden also commented on the second US-North Korea summit, which took place this week in Vietnam and broke down on Thursday without an agreement between Trump and Kim Jong Un. The negotiations reportedly broke down over what sanctions would be lifted for what degree of denuclearization.

Read more:Trump's second North Korea meeting 'clearly is a failure' as Kim Jong Un walks away with dangerous nuclear arsenal intact

The former vice president said "hard, hard, hard and consistent diplomacy" was required for tough negotiations, but he gave the president props for walking away from the deal.

"The president did the right thing by walking away," Biden reportedly said.

"But diplomacy matters, preparation matters," he continued. "The president treats everything like it's a real-estate deal."

He characterized the first summit, where Trump met with Kim in Singapore last year and the two signed a four-point agreement calling for peace on the Korean peninsula and denuclearization of North Korea, as a "great gift" to the North Korean dictator.

"He was legitimized," Biden said, according to the Journal Star. "This guy is a thug."

Biden is currently contemplating a run for the presidency in 2020, and recently he's been making stops at universities in Pennsylvania, Delaware and Nebraska.

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