In the Washington Post, Michael Gerson argues that preserving the perception that "the commander in chief is fully in command" is so important that it would sometimes be worth supporting "wrong or pointless" wars in order to maintain it. Put that way, it sounds shocking. One wonders how many human lives Gerson would sacrifice to prevent what he sees as a weakening of the presidency. Yet every time anyone argues that America must go to war in Syria because of President Obama's "red line" comments and the impact a failure to follow through would have on American credibility, the same premise is implicit: Keeping a reputation for follow-through is, for these hawks, reason enough to wage war.
This aversion to Congress contradicting the president wasn't shared by the generation that gave us co-equal branches designed to check one another. They expected that the legislature would often contradict the executive, including on matters of war, especially given the presence of both a lower and an upper body.
Jim Manzi explains at National Review (emphasis added):
The most common argument for attacking Syria is that we must maintain our credibility when the sitting president issues ultimatums (even if they are ill-advised).
The problem with this is that while the president of the United States has awesome powers under the Constitution, they do not include declaring war. He can declare “red lines” all he wants, but he can’t constitutionally commit the nation to preemptive military action in the event they are crossed. If this “loss of credibility” means in practical terms that U.S. presidents are less able to make credible insinuations that they can unilaterally commit us to wars, then this would likely result in: fewer such presidential assertions being issued; more consultation and consideration before they are issued; and more reliable delivery on the threats when the situation calls for it. Such a loss of credibility would be a feature, not a bug.
What the U.S. should signal to the world is that U.S. credibility does not rest on doing any fool thing uttered by the person who happens to be president at a given time. He or she doesn't speak for all Americans, and lacks the power to act in ways that the people and their elected representatives judge to be foolhardy. Unlike the perception Gerson wants to create, this has the virtue of being true.
It is the hawks who threaten American credibility most in the long run, both because they'd make us subject to any chance comment from the series of fallible politicians who make it to the White House, and because waging an ill-conceived war, with all the attendant negative consequences, hurts the credibility of a nation a lot more than any mere rhetoric. When we look back at blows to American credibility, we think of Vietnam and Iraq, not some bit of rhetoric and the way the world interpreted our follow through. If an American intervention in Syria goes badly, our credibility will suffer profoundly, and hawks will once again bear blame for weakening America more than any other Americans.
Nothing weakens a country like an ill-conceived war.