There has been a great deal of talk in U.S. foreign policy circles about “red lines” and the strength of American resolve in recent days. Much of it has revolved around the emerging evidence that chemical weapons, namely sarin gas, may have been used in the Syrian civil war, which drew attention back to the Obama administration’s declarations in 2012 that the use of unconventional weapons could be a trigger for American intervention in that conflict. The sarin discussion came on the heels of a brief controversy surrounding allegations made by Chinese dissident Chen Guangchen that the Chinese government was not living up to the commitments it made to the United States to end the diplomatic standoff in May 2012 after Chen sought refuge at the U.S. Embassy in Beijing.
Both episodes were cited by critics to accuse the Obama administration of undermining U.S. credibility by not taking more forceful action, whether to become militarily involved in Syria or to put greater pressure on Beijing. As a result, according to this argument, the administration is sending a signal of American weakness that will dishearten friends and encourage rivals.
Red lines are always most effective, however, when there is already a pre-existing commitment to act. In such cases, the red line serves as a clear warning to others of the dire consequences that will result if the line is crossed—consequences that the issuing state has already thought through and accepted. The two most famous red lines in recent history—Berlin during the Cold War and the Demilitarized Zone separating the Koreas—have been effective because the presence of U.S. forces acting as a proverbial tripwire guaranteed an immediate military response on the part of the United States and all but ensured that any initial provocation would be met by an escalated response.