Donald Trump and his administration made two key mistakes which helped contribute to his summit this week with the leader of North Korea falling apart, according to the top Democrat on the Senate Armed Services Committee.

However, Trump was right to walk away from the table in Hanoi when he did. That was according to a separate interview with Bill Richardson, who served as United Nations ambassador during the Clinton administration and also personally involved himself in diplomacy with leadership in North Korea, which has long been an extremely impoverished, pariah nation.

Trump this week travelled to Vietnam for his second face-to-face meeting with Kim Jong Un, in an attempt to reach an accord to end the North’s long-standing nuclear weapons and missile programs. It was the second such meeting for the pair, following their first summit last year in Singapore.

The meeting abruptly fell apart on the second day with no agreements in hand.

Going into the summit, Trump and his team made two “critical mistakes,” said Sen. Jack Reed of Rhode Island, ranking Democrat on the Senate Armed Services Committee.

“Despite the great work of the Special Envoy Steve Biegun to set the meeting up, there was no detailed listing of the nuclear sites and the nuclear facilities that are really the heart of our discussions,” Reed explained. “Typically for a meeting–and President Reagan had many meetings with [Soviet leader Mikhail] Gorbachev, but they went in with pretty detailed guidelines or pathways that they were going to pursue. They didn’t have this in this case.

“The second mistake in Singapore, President Trump, I think, sent the signal to Kim Jong-un that this is all going to be a one-on-one private conversation,” Reed added. “‘You can ask me and I’ll give it to you.’ Particularly with respect to the military exercises. When the president conceded, off the cuff, that we wouldn’t have military exercises–in fact, described them as provocative war exercises [at the Singapore meeting], I think that sent the wrong signal to Kim Jong-un. I think he said, ‘I don’t need this preliminary negotiations, I’m just going to sit down with him and ask him to take off sanctions, he’ll probably do it.’ And so, the setting was all wrong.”

The result was a miscalculation, Reed added.

Despite everything, Trump was right to leave when he did. That’s according to Bill Richardson, who served as United Nations ambassador in the Clinton administration, and is someone who personally himself engaged in diplomacy with North Korean leadership over the years.

“It was a setback for both sides, but I think the president was right in walking away,” Richardson said, adding that the strongest tool that the United States retains in negotiations with North Korea is economic sanctions.

“The reality is that I don’t think North Koreans were ready to take any significant steps to dismantle. That is the keyword. … They were ready may be to freeze some of their nuclear facilities, destroy one, which I have been to. I don’t think it’s that significant anymore.”

Secretary of State Mike Pompeo is correct that the two nations should allow negotiations to continue, Richardson said.

“You’ve got to keep negotiations going. At a lower level, not on the presidential level,” Richardson added.

Reed and Richardson each made their remarks during separate segments on Fox News.