Suzanne Maloney talks sense to people promoting the “attack Syria to warn Iran” argument:

There is just one catch: to think that a strike on Syria would send a message to Iran is to fundamentally misread the Iranian psyche. Doing something in Syria may make sense on the merits, especially if it would help resolve the civil war. But using Iran as a justification would be disingenuous and even dangerous. It would be almost as irresponsible as the trumped-up intelligence that Obama’s predecessor used to drum up support for the Iraq war a decade ago [bold mine-DL].

Invoking Iran is useful for many Syria hawks because they have already put an enormous amount of effort into building up and exaggerating the threat from Iran, and it allows Syria hawks to exploit fears of Iran’s nuclear program to try to generate support for an attack that would most likely make the nuclear issue harder to resolve without resorting to force. Linking Syrian chemical weapons and Iran’s nuclear program also reflects the widely-held assumption that Iran is inevitably going to acquire nuclear weapons unless something is done to stop this. That is likely wrong and distorts the entire debate over Iran policy in the West, but that is a topic for another post.

As Maloney explains, the Iranian government sees U.S. policies in the region simply as proof of hostility towards Iran:

As a result of this history, the American debate over military strikes against Assad doesn’t factor into U.S. credibility with Iranian leaders on nonproliferation; it merely confirms their long-held paranoia that Washington is determined to undermine Iran and will use any means to destabilize the broader Middle East for its own nefarious purposes [bold mine-DL].

Imagine for a moment that the U.S. were in Iran’s position: a much more powerful government hostile to ours had waged two wars of regime change on our borders, it defined its policy towards our country solely in terms of grossly exaggerated fears of the threat that we ostensibly posed to them, most of the surrounding region was filled with governments aligned against ours, and one of our only remaining allies on the planet was threatened with attack from that same government. Wouldn’t we see this government as deeply hostile to us, perceive it as a major threat to our security, and do what we could to discourage an attack on our country? In such an environment, hard-liners would usually benefit and prevail in internal policy debates. If Iranian hard-liners benefit from an attack on Syria, the effect will be the opposite of the one that many Syria hawks predict, and it will make it that much more difficult to reach an agreement on the nuclear issue.