Democratic Sen. Chris Coons of Delaware said President Trump's summit with North Korean dictator Kim Jong Un in Singapore last month was "not much more than a reality TV handshake" after North Korea compared Secretary of State Mike Pompeo to a "gangster" following talks in Pyongyang. Coons says that members of Congress have not yet received a briefing or detailed strategy for just how North Korea intends to commit to denuclearization of the Korean peninsula as Kim and Mr. Trump left the summit last month agreeing to find a path forward.

"My concern is that the Singapore summit last month was really not much more than a reality TV handshake summit that didn't really accomplish much in terms of getting North Korea to commit to verifiable and irreversible denuclearization," Coons said on "Face the Nation" Sunday.

"I far prefer diplomacy to Twitter threats and commend Secretary Pompeo for how hard he's trying to make something out of nothing," he continued, "but so far I don't see that we've accomplished much and my concern is that President Trump unilaterally gave away doing our military activities with our vital allies, South Korea and Japan, without consulting with them, and we got nothing but empty promises of denuclearization from Kim Jong Un."

As Mr. Trump prepares to head to Brussels for a meeting of the NATO alliance, Coons also expressed concern that the gathering will be a repeat of the G7 summit in Canada, where Mr. Trump backed out of an international agreement over ongoing trade disputes with allied partners.

"I'm concerned, Margaret, that instead what we're going to see is a repeat of last month's show where President Trump went to the G7 summit in Canada and put a thumb in the eye of the prime minister of Canada and picked fights with our vital allies on tariffs and trade and on security issues and then went to Singapore for a summit with Kim Jong Un that as I just said didn't produce much," said Coons.

Coons said he's worried Mr. Trump will employ a similar tactic ahead of his meeting with Russian President Vladimir Putin in Helsinki, Finland.

"My concern is he'll continue to stir the pot with NATO, undermine the credibility of our commitment to mutual security that is at the core of NATO, and then go to Helsinki for a summit with Putin where I'm very concerned about what things he might give away or what things he might say with Vladimir Putin, who really is a core adversary of both the United States and the NATO alliance," Coons added.