Tim Marshall describes the “underwhelming” evidence that chemical weapons were used in Syria:

However, it is not known who had the soil samples before they were passed to the British, and the MoD will not publish its findings.

Given the debacle over the use of intelligence in the Iraq War, its reluctance to go public with information suggests it is not sure of its veracity but there is also the problem that publishing even limited evidence risks compromising sources inside Syria.

It’s a similar story in the US where even the most hawkish member of the Senate, John McCain, agrees that the evidence “may not be airtight”.

Since the evidence that chemical weapons were used is so weak, it is impressive how confident so many people are that a “red line” has been crossed and U.S. “credibility” on its other commitments elsewhere in the world has somehow been compromised. John Bolton doesn’t even favor intervention in Syria, but he is sure that “failing” to enforce a “red line” in Syria will encourage Iran and North Korea, among others:

What has changed, if Mr. Obama allows his red line to be crossed unanswered, is that his latest act of foreign-policy fecklessness provides further proof to Iran, North Korea and other adversaries, whether states or terrorists, that he is not a force to be reckoned with.

It would be easy enough to ignore this if it were just another tiresome Bolton op-ed. Unfortunately, there are many other people chiming in with the same shoddy argument. Despite the fact that none of the Western governments making the “underwhelming” claim about sarin use can say with much certainty what happened or who was responsible, some observers seem to possess great certainty about what a “failure” to respond to possible small-scale use of a chemical weapons means for unrelated issues of potential nuclear proliferation in Iran and tensions on the Korean Peninsula. The essence of this argument is that other governments will be less intimidated by U.S. military threats if the administration doesn’t “act” to enforce a fairly vague threat by doing what Syria hawks have wanted him to do for two years.

It would be giving this argument too much credit to call it simplistic. U.S. security guarantees to South Korea and Japan do not depend on anything that the U.S. does or doesn’t do other parts of the world, except insofar as new unnecessary wars limit the resources available for the defense of these allies. The U.S. position that Iranian acquisition of a nuclear weapon is “unacceptable” has been stated so often and backed up by so many coercive measures over the last decade that one has to believe that a handful of presidential utterances on an unrelated issue count for more than a decade’s worth of official policy on the issue in question. One can think this position is a good one, or one can think that it is a recipe for future disaster, but the credibility of threatened U.S. military action against Iran does not depend in any way on whether the administration backs up its “red line” rhetoric on Syria. It is possible that intervening in Syria could derail negotiations with Iran, and it is possible that yet another U.S.-backed push for regime change will make the Iranian leadership even more obsessed with preserving their own hold on power, but unfortunately the U.S. threat to attack Iran is only too credible and will remain so regardless of what the administration does in Syria.