A debate over the effectiveness of U.S. sanctions against North Korea -- and China's role in making them work -- broke out between members of Congress and a senior Defense Department official at a House Armed Services Committee hearing on Tuesday.

It was the latest illustration of an ongoing disagreement between the Trump administration and many members of Congress, from both political parties, over how much pressure Washington should be putting on Pyongyang in order to achieve the elusive goal of denuclearization.