Despite faltering denuclearization talks, U.S. President Donald Trump has been heaping praise on North Korean leader Kim Jong Un, brushing away concerns by top Asian allies over recent missile launches and boasting of his "very good" relationship with the dictator of the nuclear-armed pariah state.

In contrast, South Korean leader Moon Jae-in has been feeling the heat from the tempestuous Trump as the two allies wrangle over how much Seoul should pay to keep 28,500 American troops on the Korean Peninsula. In the face of Trump's campaign to pressure allies to dole out more cash for their presence, South Korea boosted its share by more than 8 percent this year to $924 million in what is called the Special Measures Agreement.

This time, however, Trump wants the South Koreans to pay even more.