While Trump has worked to thaw relations with Kim over the last year, including through an unprecedented face-to-face meeting in Singapore, North Korea is reportedly still working on new missile development projects. In July, an NBC News report, citing U.S. intelligence assessments, said that North Korea had increased production of fuel for nuclear weapons at multiple secret sites in recent months.
Meanwhile, under Kim, the reclusive state has conducted its most powerful nuclear test, launched its first-ever intercontinental ballistic missile and threatened to send missiles into the waters near Guam.
Since 2011, North Korea has fired more than 85 missiles and conducted four nuclear weapons tests — which is more than his father, Kim Jong Il, and grandfather, Kim Il Sung, launched over a period of 27 years. As it stands, North Korea is the only nation to have tested nuclear weapons this century.
Read more: A timeline of North Korea's defiant rocket launches in 2017
The Pentagon did not immediately respond to CNBC's request to comment.
The second meeting extends a turn toward diplomacy after Trump and the North Korean regime made repeated threats in the early months of the U.S. president's tenure. As Pyongyang continued testing missiles, Trump said in August 2017 that North Korea "will be met with fire, fury and frankly power, the likes of which the world has never seen before."
On New Year's Day 2018, Kim — who Trump once labeled "Little Rocket Man" — said he had a nuclear launch button ready at his desk at all times. The president responded by tweeting: "I too have a Nuclear Button, but it is a much bigger & more powerful one than his, and my Button works!"
The two leaders have recently been more conciliatory. Even though reports showed reasons to doubt North Korea's commitment to denuclearization, Trump heaped praise on Kim last year. In September, Trump said the two leaders "fell in love" after exchanging "beautiful letters."
Trump has defended his first summit with Kim as necessary to preserve peace, after critics said he legitimized a dictator with a dismal human rights record.