Conventional wisdom has it that New START matters only at the margins, fitting comfortably within projected U.S. and Russian strategic plans, foreclosing nothing of substance and costing the usual ransom to assuage skeptics. I’m not buying this line of argument.

The Senate’s consent to ratify New START matters a great deal. To understand why, consider the likely consequences if irreconcilable Republicans are able to block ratification. Their arguments for doing so are so strained that foreign capitals would be justified in concluding that Washington has lost its bearings. America’s standing in the world would take a dive. Friends and allies would count less on Washington. Troublemakers would have more room to maneuver. The currency of international power would continue to flow towards Beijing, and there would be no agreed rules for reductions and verification arrangements for the two largest nuclear arsenals.

These arguments for New START are familiar. With some variation, they date back to the old SALT debates. I remember traveling to Missoula, Montana and elsewhere to champion the merits of the SALT II Treaty. The Carter administration, in which I served, lost this debate for three primary reasons: The strategic balance seemed to be tipping in the Kremlin’s favor, Moscow appeared to be emboldened as a result, and SALT II’s accomplishments were modest. After the 1972 SALT I Interim Agreement opened the barn door for MIRVs, by the time they were rounded up seven years later in SALT II, the numbers weren’t pretty.

The arguments against New START also date back to the SALT debates. They were far more persuasive during the Cold War. Russia is not the former Soviet Union; its Gross Domestic Product is approximately the size of France. Arguments that Moscow has negotiated the United States into a corner lack credibility. In the SALT era, the Anti-Ballistic Missile Treaty strictly limited national missile defenses. The ABM Treaty is now dead, and New START doesn’t revive it. Back in the day, critics of arms control argued, with good reason, that SALT was too permissive. Now they fret, without good reason, that the reductions mandated by New START are too constraining.

The Senate’s vote on New START will speak volumes. It’s hard to lead globally by just saying “no.” The United States needs an internationally-minded Republican Party, one that supports diplomatic efforts to reduce nuclear dangers. How can the United States step confidently into the nuclear future if Republican Senators are so fearful of New START?