Trump may be eager to change the subject and some foreign policy experts fear that could prompt the president to make a significant concession or strike an attention-grabbing deal - such as a declaration to formally end the Korean War, which has been suspended in an armistice since 1953 - without extracting much in return from Kim.
A landmark first summit between Mr Trump and Mr Kim in Singapore last June led to a promise by Mr Kim to work towards complete denuclearisation on the Korean peninsula.
While Biegun worked for decades as congressional staffer and as a White House foreign policy aide under President George W. Bush, his latest appointment was initially greeted with skepticism, given he was primarily a Russian Federation specialist with little exposure to the complex North Korea problem.
Before that freeze, the North conducted a series of tests that it says has given it powerful nuclear bombs and missiles capable of reaching the US mainland. He stressed that the USA will not ease the sanctions until a complete denuclearization of North Korea is achieved. DPRK is an abbreviation of North Korea's official name, the Democratic People's Republic of Korea.
"North Koreans have no sense of humor", the impersonator told reporters before heading to Hanoi's airport to leave the country. Stephen Biegun, the USA special envoy for North Korea, said earlier this month that Trump was "ready to end this war", fueling speculation that the formal end of the conflict may be near. The two leaders are expected to discuss worldwide sanctions on North Korea and Pyongyang's nuclear arsenal.
Trump told the press on Wednesday that his trip to Vietnam would be "very successful", anticipating his two-day meeting with Kim would "accomplish a lot".
"The possibility is open, Eui-kyeom said, referring to the results expected from the Trump-Kim summit meeting scheduled for February 27-28".
Michael Cohen to Accuse Trump of Criminal Conduct in Televised House Hearing
However, as a convicted perjurer, Cohen must convince numerous same lawmakers he lied to that he is telling the truth this time. Cohen is expected to come to the congressional hearing with documents and other visual aids to support his contentions.
One memorial site in Sinchon - where USA forces are said to have massacred more than 35,000 people, although foreign researchers say the toll is unclear and there is no evidence of American culpability - features a "revenge-pledging place" where busloads of visitors can hurl abuse at the US.
North Korea wants an easing of punishing USA -led sanctions, security guarantees and a formal end of the 1950-1953 Korean War, which ended in a truce, not a treaty.
Biegun has said he will be seeking both in Hanoi and will also be looking to agree a road map for a possibly lengthy post-summit negotiation process.
South Korea's Yonhap news agency said Kim's train had passed through a station in China's port city of Tianjin, southeast of Beijing, at around 1 p.m. (0500 GMT).
Officials in Washington and Seoul have said possible steps forward could include allowing inspectors to observe the dismantlement of North Korea's Yongbyon nuclear reactor and opening U.S.
Hours earlier, he ended a tweet about the summit by posing the key question that looms over their meeting in Vietnam: "Denuclearization?"
Vietnam has released few details about arrangements for the summit including its specific venue or timing.