This study analyzes the political viability of the Russia-North Korea-South Korea (RNS) gas pipeline project. This analysis demonstrates that North Korea’s fourth nuclear test in January 2016 changed the dynamic of the project. Before the test, when inter-Korean relations were good, South Korea and Russia could make efforts to secure political support for the project. However, after the fourth nuclear test, this was no longer the case. As North Korea’s nuclear power status became more evident, this nuclear problem began to have profound implications for U.S. security. In response, Washington not only led the UN Security Council to impose very severe sanctions against North Korea, but also placed its own sanctions on the country. These sanctions began to contain provisions that could prevent the implementation of the pipeline project. In addition to these sanctions, the U.S. sanctions against Russia in 2017 over its intervention in the U.S. election and aggression against Ukraine also contained clauses that could hamper it. Therefore, unless the U.S. lifts or eases all of these sanctions, South Korea and Russia are unwilling to take any concrete actions to secure political support for the RNS pipeline project. Based on this analysis, this paper argues that the U.S. now holds the most important key to its political viability.