"Our whole relationship with North Korea and the Korean Peninsula will be very different to what it has been in the past".
The talks came amid an inter-Korean detente and a thaw in relations between the United States and the North.
Secretary of State Mike Pompeo conveyed USA resolve for "complete, verifiable and irreversible denuclearization" of the Korean Peninsula with Chinese President Xi Jinping, the State Department said on Thursday, as well as concerns about Chinese activities in the South China Sea.
Mr Trump also announced a halt to wargames between the United States and South Korea and expressed a desire to bring USA troops home, which left a former South Korean general "speechless".
What the top diplomat is doing, including his trips to DPRK's two neighbors immediately after the historic US-DPRK meeting, have drawn widespread attention, as Pompeo is charged by US President Donald Trump with leading follow-on negotiations with the DPRK.
Michael Green, who was Asia director on the National Security Council staff during the George W. Bush administration, said the likely damage from suspending drills is multiplied by Trump's failure to inform South Korean and Japanese officials in advance and his focus on cost-savings.
There will be no sanctions relief for North Korea until its complete denuclearization, U.S. Secretary of State Mike Pompeo has said in Seoul.
News coverage of the Singapore summit
Axios reports that Israel's foreign ministry recently issued a report that casts doubt on the significance of Trump's meeting with Kim in Singapore.
Later, the South Korean delegation chief sought to put a positive spin on the talks.
"The No. 1 problem with this, geopolitically, is that it suggests to our allies that we are just incompetent, that we don't recognize the threat", Green said. "There is no longer a Nuclear Threat from North Korea".
"Making unnecessary and unreciprocated concessions is not in our interests - and it is a bad negotiating tactic", McCain said.
The job of USA ambassador to South Korea has been vacant since Trump took office in January 2017, a point of bipartisan consternation given the need for strong collaboration with Seoul during the sensitive nuclear discussions. -South Korea military exercises have been carried out twice in spring and fall each.
President Donald Trump saluted North Korean general and defense minister No Kwang Chol during the Singapore summit, as seen in a video released by the country's state media. But if we know one thing about negotiations in general, and negotiations with North Korea, it is this: If you can't write it down, you don't have a deal.
"That is the backbone of the US-South Korea alliance".