JUST a decade ago, a short season in the ebb and flow of global influence, economics was in thrall to the Washington consensus and geopolitics was a wholly owned subsidiary of the hyperpower run out of the White House. Today, before launching an attack to punish Syria’s Bashar Assad for using chemical weapons, Barack Obama has felt bound to seek the blessing of Congress (see article). Britain has failed to stand alongside its closest ally (see article). The Middle East echoes to talk of America’s diminished leadership. And one of Mr Obama’s aides has briefed that the strike will be “just muscular enough not to get mocked”.

America has often let atrocities go unpunished before. In the 1980s it sent no missiles when Saddam Hussein gassed Kurds and Iranians; nor did it do so when Mr Assad’s father, Hafez, massacred as many as 20,000 of his own people. But that was back in the cold war, when Saddam was fighting Iran and before the ban on chemical weapons had been buttressed by a UN convention. Moreover, Mr Obama declared last summer that he would not tolerate Syrian use of chemical weapons. With more than a thousand dead in a nerve-agent attack that, it now turns out, was just the latest of many, the president rightly concluded that Syria was testing America’s capacity to impose its will.

This makes the congressional votes and the action to follow one of those episodes that will define America’s—and the West’s—place in the world. It will signal what is left after the hubris of Iraq and unfathomable complexities of Afghanistan. Amid challenges from Russia and Iran and the growing weight of China, both as an economic power and a champion of authoritarian purpose (as opposed to democratic indecision), it is also a measure of the West’s self-belief. The world is watching. Allies and foes alike will shape their behaviour around the expectations that this moment sets in train. It is vital, therefore, that America not only acts, but acts for the right reasons.

Baghdad baggage

This newspaper has argued that America and its allies should give Mr Assad one chance to renounce his deadly chemicals and, if he demurs, hit him hard. The purpose would not be to bring about regime change, but to re-establish deterrence and because Mr Obama must be seen to stand by his threats. Inaction will encourage Mr Assad to use yet more chemical weapons. Tyrants and proliferators everywhere, including Iran and North Korea, will be emboldened.

The hope is that Congress will for once put principle before partisanship and support the president. Joined by France, which all along has been admirably resolute, Mr Obama could then strike the regime in Damascus with an attack severe enough to bury any thought of mockery. That would be good. Yet the way Mr Obama is going about this operation is flawed, both in his choice of a congressional vote and in his rhetoric.

The vote in Washington has short-term merits for Mr Obama. Most Americans seem to be against striking Syria (as are most of the British and French). Here is a chance to establish the legitimacy of a strike and dip Republican hands in the blood. But at what cost? There is the possibility of losing the vote, of course—a real presidency-wrecking risk. But even with a victory in Congress, Mr Obama will have weakened the credibility of foreign policy, the very thing that he wants to safeguard. The executive needs to be agile and quick when dealing with the world. The president sometimes needs to take hard and unpopular decisions. Mr Obama insists that his choice to consult the legislature does not curtail that freedom. But this is an operation designed to bolster deterrence. Mr Obama’s request creates expectations that future enforcement will also be subject to the vagaries of congressional sound bites. That tends to weaken deterrence.

Mr Obama may retort that he is dealing with the legacy of George W. Bush. This has left Americans (and the British and French) with an abiding scepticism about the use of intelligence and the purpose of intervention. The West has paid for the campaigns in Iraq and Afghanistan with trillions of dollars of taxes and thousands of their soldiers’ lives. Even if they dislike saying it out loud, many Americans doubt that Muslims have much disposition for Western values like democracy and tolerance. Why try to be the world’s policeman if it is not just a thankless task, but a hopeless one?

The vision thing

These sceptics are fighting the last war. Syria is not Iraq. The evidence that the regime has committed atrocities is clear beyond doubt. Even if Mr Assad defies America after a strike by unleashing yet more sarin, Mr Obama is not about to invade.

The arguments for intervening in Syria are narrower and less Utopian than they were in Iraq. First is the calculation of American interests. The international arena is inherently anarchic. Only laws and treaties that are enforced impose any order. By being the world’s policeman, America can shape the rules according to its own interests and tastes. The more America steps back, the more other powers will step in. If it is unwilling to act as enforcer, its own norms will fray. If it is even thought to be reluctant, then they will be tested. China already prods at America; Vladimir Putin’s Russia has begun to confront it—and not only over Syria. Whether Syria was a vital American interest before this attack was debatable, but not after Mr Assad’s direct challenge to Mr Obama’s authority.

Second is a reaffirmation of Western values. America’s potency comes not just from its capacity to project force, but also from the enduring appeal of the values invoked by its founders. Those are stronger than Mr Obama seems to think. With China’s economy slowing and its political corruption evident, the Beijing consensus will seem ever less enticing to citizens of the emerging world. Mr Bush tainted America’s values with inept invasion, prisoner abuse and imperial overstretch. Meeting Mr Assad’s atrocities with appropriate force will help to rebuild American moral authority in the world. If Congress must be involved, it should send that message just as loud and clear as it can—and so should Mr Obama’s allies.