China is not afraid to use its influence on the Korean peninsula to protect its interests against the U.S., which is in the process of deploying a missile defense system in South Korea. Beijing says the system is a security threat and has retaliated against major South Korean businesses.
"I think Moon wants to establish a good, working relationship with Trump, but they have some different ideas," said Robert Manning of The Atlantic Council.
Trump and Moon are set to meet for the first time Thursday and Friday at the White House.
Moon was elected in early May, ending months of leadership uncertainty in the country after President Park Geun-hye was impeached and arrested for alleged corruption. Moon campaigned on taking a more conciliatory tone in dealing with North Korea and earlier this month officially suspended deployment of the Terminal High Altitude Area Defense system, or Thaad.
Trump clashed with South Korea in an April interview with Reuters by saying the country should pay for the $1 billion Thaad system. Trump also said the U.S. should renegotiate or terminate its trade deal with South Korea.
The "South Korean government doesn't want Thaad to be the official agenda for the summit meeting," said Hyun-Wook Kim, professor at the Korea National Diplomatic Academy in Seoul.
He's watching whether the key missile defense program and flashpoint for China will even be part of Moon's and Trump's joint statement.
Meanwhile, Trump is reportedly growing increasingly frustrated with China. His relationship with Beijing had improved after Chinese President Xi Jinping visited in April, but Trump still threatened to use trade policy to get China to act on North Korea.
Trump "seems to have over-estimated his personal bond with Mr. Xi," The Economist said in its June 24 issue. The President is "telephoning [Xi] so often to ask about Korea co-operation that Chinese officials grumbled to American contacts that their president is 'not our North Korean desk officer.'"
On June 20, Trump tweeted that "while I greatly appreciate the efforts of President Xi & China to help with North Korea, it has not worked out."
Analysts also worry that Trump may disrupt the meeting with tweets, or a cold persona as was the case in his meeting with German Chancellor Angela Merkel.
"With the North Korean security threat looming larger and larger, good chemistry between President Moon Jae-in and President Trump is essential," Thomas Byrne, president of The Korea Society in New York.
The U.S. and South Korea do agree that China is important in working towards North Korea denuclearization.
"In principle, I think they can get along as far as North Korea is concerned," Hyun-Wook Kim said. Moon "understands this is not the right time for dialogue."