If the United States does not act in Syria, that could signal a turning point in international relations. We could witness, in effect, a self-imposed American version of what happened to France, and, much more dramatically, Britain, in the failed 1956 Suez campaign.
Although President Barack Obama is gaining congressional support, the Washington Post estimated on Tuesday that there were still twice as many members of the House of Representatives committed to vote against, rather than for, the resolution. Opinion polls also demonstrate overwhelming public opposition.
So American inaction remains a real possibility.
Mr Obama has clearly placed his own domestic and international credibility in grave peril. But the vote will reflect on the standing, and credibility of the United States itself. And not only in the Middle East but globally.
The analogy with the British fiasco in Suez is both compellingly similar and strikingly different. In the 1956 campaign - launched in a secret plot hatched with France and Israel to reverse Egypt's nationalisation of the Suez Canal - Britain attempted to assert its age-old imperial role.
What Britain did not realise until it was too late was that it had overreached. Their era had passed, and was now superseded by a new order: the Cold War defined by American power in competition with the Soviet Union.
The old colonial forces then still had the desire, but they lacked the means to enforce their will.
Should the United States decline to act in defence of international order in Syria, as recently endorsed by the Arab League, and not respond forcefully to the abominable use of chemical weapons by the Damascus dictatorship, the international order could witness a similar outcome from the opposite conundrum.
The United States clearly retains the means to intervene in global crises. But does it still have the will?
The American people are experiencing a profound sense of "Middle East fatigue", following the debacle in Iraq, a failed nation-building effort in Afghanistan and a lingering economic crisis back home. This accounts for the extreme opposition in American public opinion, and, perhaps, the House of Representatives, to authorising even limited military action in Syria.
If that sense of exhaustion comes to define a passive reaction to the outrage in Syria, it will almost surely signal the beginning of the end of the era of American regional leadership in the Middle East. Whatever their interpretations of the Suez catastrophe, almost all British historians regard it as symbolising not only the end of British hegemony in the Middle East, but also of Britain's global role.
Thereafter, it could play only a supporting part to the American lead. Elizabeth Monroe famously described it as the end of "Britain's moment in the Middle East", after which it could not wield much regional influence because, simply, "the power behind it was permanently impaired".
This was objectively true of Britain in the 1950s. But it is objectively untrue of the United States at the moment.
However, since the 19th century a wide range of Americans from Mark Twain to Gore Vidal have pitted "republican virtues" against "imperial decadence", and bemoaned the fact that the United States became an international "great power".
A contemporary strain of neo-isolationist, America-first thinking has become extremely popular on both the left and the right. It could lead to a voluntary surrender of American leadership and credibility in the Middle East by refusing to act in Syria now and following that inclination to its logical conclusion. This would mean, essentially, the end of "America's moment in the Middle East", although prematurely and wilfully.
If the United States voluntarily walks away from its will to act in the Middle East, what, short of direct attacks against American targets, would make it more inclined to be assertive elsewhere? In other words, this would likely be the precursor to a more thoroughgoing end of the "American moment" globally.
When the Suez crisis demonstrated the impotence of the traditional European colonial powers, an old order died. But it had already been replaced by a fully formed new one: the American-Soviet rivalry of the Cold War.
The greatest danger with the potential "American Suez" in Syria is not just that it could signal the beginning of the voluntary international retreat of a power that tends, when it can, to promote reasonable values. Worse, there is nothing already at work to take the place of a Middle Eastern regional, and indeed global, American-led order.
Whether the ensuing free-for-all and scramble for power would look more like Hedley Bull's Anarchical Society, in which international communities somehow find rules because they need them, or Thomas Hobbes' Leviathan, in which the lack of a clear leader produces "the war of all against all", is unknowable. But that uncertainty in itself is cause enough for alarm.
It's not just in the interest of Americans that they overcome their understandable reticence and accept the responsibility to act in Syria, thereby implicitly recommitting to act as guarantor of the global order. It's also in the common interest because the international community is not ready for a post-American era.
Mr Obama has made a gamble that, at least in Congress, will probably pay off. The possibility that Americans might be imposing a "Suez moment" on themselves appears to be receding. But, the implications of even the prospect this might - and still could - happen ought to be sobering to all.
Hussein Ibish is a senior fellow at the American Task Force on Palestine in Washington, DC
On Twitter @ibishblog
