Canny U.S. diplomacy, or barely redeemed gaffe? Russian opportunism, or sincere effort to stave off war? Syrian feint, or desperate gambit by a regime running scared? Whatever one thinks about how the U.S. and Russia reached their agreement to destroy Syria’s chemical weapons arsenal, one thing is clear: It couldn’t have been achieved in the absence of a strong international consensus against the use of chemical weapons.

Strengthening the ability of the United Nations to identify and enforce the world’s collective will should be high on President Barack Obama’s foreign policy agenda, beginning with his trip tomorrow to the UN General Assembly.

Widespread support for the Chemical Weapons Convention gave the U.S. a rallying point for its effort to hold Syrian President Bashar al-Assad accountable for brutalizing his people. It also gave Syria and its patron Russia a face-saving way to avert a U.S. strike: They weren’t knuckling to pressure; Syria was merely signing a treaty that almost all of the world’s nations had already joined. On paper, at least, that outcome is exactly the kind of result hoped for by champions of collective security.

For the U.S., this peacekeeping impulse can reduce the need to spend diplomatic capital or deploy military might. Yet two obstacles make the UN less effective than it could be: first, a creaky Security Council that has become paralyzed by division; and second, the U.S. tendency to punt on treaties or to exempt itself from provisions it doesn’t like.

The fight over the text of a Security Council resolution on the enforcement of the Syria agreement is the latest evidence of the stalemate among its five permanent members. Since 2011, Russia and China have vetoed three resolutions on Syria, with Russia also preventing a vote on resolutions condemning chemical attacks and calling for humanitarian relief efforts.

Granting the permanent members a veto was the price of getting them to endorse collective security in 1945. Yet Security Council membership now represents a much smaller slice of the world’s population and leaves out big economic players such as Japan and Germany (the second and third biggest UN funders) as well as emerging powers India and Brazil. Even by the council’s most important criterion -- the ability to safeguard international peace -- the current membership comes up wanting.

How to expand the council is one of the most critical challenges facing the United Nations. You won’t find any mention of it, however, in Obama’s four previous speeches to the annual General Assembly. The U.S. should be leading the campaign to build consensus on the process for admitting new members, what the mix of permanent and elected members should be, and what powers they should have.

Yes, it is a thorny issue. Yet there are ways of safeguarding the interests of the existing permanent members while strengthening the Security Council’s legitimacy. At the very least, it is a goal commensurate with U.S. power and influence. The longer the U.S. waits to begin, the more ineffective and illegitimate the Security Council will come to seem, and the more U.S. interests will be damaged.

The U.S. can also help its cause by not taking such an a la carte attitude toward norms, treaties and international obligations. The national exemptions carved out by U.S. legislators from the Chemical Weapons Convention are a case in point. Saying the U.S. can refuse challenge inspections or the use of international labs to test samples makes it harder to enforce those requirements on others, just as failing to ratify the Comprehensive Test Ban Treaty -- as Obama pledged the U.S. would do in 2009 -- makes it harder to enlist other countries in the fight against nuclear proliferation. Increasingly, the U.S. must weigh its neuralgia about national sovereignty against the benefits that can come from pooled sovereignty, when states agree to share decision-making powers.

Sometimes the U.S. has to take on the so-called international community to do what’s right -- for instance, the fight against the UN General Assembly’s infamous 1975 “Zionism is a form of racism” resolution. (The U.S. eventually won that battle in 1991.) Other times -- as recent weeks have shown -- it takes the threat of unilateral U.S. action to get the UN and the rest of the world to uphold the principles they claim to honor.

Yet the basic point holds: More international agreement is better than less, and more ways of encouraging and enforcing it are better than fewer. As the benefits of the global taboo against chemical weapons have shown, the U.S. has more to gain than to lose from the support of robust international norms.

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