President Obama said Sunday that the U.S. could pull its support from South Sudan if there is a revolution. Four U.S. service members were wounded Saturday when gunfire erupted during a mission to evacuate American citizens from Bor, the capital of the region. It’s unclear who was responsible for the attack. “Any effort to seize power through the use of military force will result in the end of longstanding support from the United States and the international community,” the White House said in a statement. An official in the region said Americans did not tell Gen. Peter Gadet, the top commander in Bor who reportedly defected from the South Sudan military last week, that their forces were coming in, which may have led to the attack.