Even as North Korea discloses a new uranium enrichment facility and Iran moves toward a nuclear breakout, President Obama and America’s liberal foreign policy establishment are demanding ratification of a treaty that will dramatically weaken our defenses against nuclear assault.

The new U.S.-Russia START treaty being rushed through the Senate by the White House could stymie our defenses against nuclear threats from North Korea and Iran, hand Russia a tactical nuclear advantage, and further diminish our nuclear arsenal’s declining credibility.

The new treaty is meant to replace the previous START treaty between the U.S. and Russia, which expired last year. Supporters say the new pact should be ratified, which requires approval from two-thirds of the Senate, in order to eliminate more strategic warheads and resume inspections of Russian nuclear sites.

But the treaty is fatally flawed. It will impede the best thing to make nuclear wars less likely: ballistic missile defenses. Aspiring nuclear powers like North Korea, and established ones like Russia, will be less inclined to develop or use nuclear missiles if they can be shot down in flight. But the pact’s language calls for cuts in U.S. missile defenses. The reductions would be required even as North Korea and similar regimes that proliferate weapons work assiduously on nuclear bombs and missiles to strike the U.S. and our allies directly.

The Obama administration has downplayed this, claiming that the anti-missile-defense language is only in the treaty’s preamble. But the Russians have indicated they view the language as binding, and there are further limitations on missile defense in Article V of the treaty. -- These deep concessions to Moscow by the Obama administration reflect the lingering dislike of missile defense by liberals and the Washington foreign policy establishment.

In addition, the treaty does not address tactical nuclear weapons, where Russia holds a significant advantage over America. The Obama administration appears to have intentionally ignored this detail in its rush to ‘get to yes’ with Moscow. Russia will forgo a small number of strategic arms it probably would have retired anyway, while remaining dominant in the nuclear systems that matter most in today’s world.

Advocates say the treaty’s verification provisions are a reason to rush passage, as access to Russia’s nuclear sites has been curtailed since the last agreement lapsed. But the new pact is relatively unverifiable.

Specifically, it has fewer mechanisms for monitoring than the last START treaty, including concessions to the Russians in sharing telemetry, thoroughness of inspections, verifications of ICBMs and submarine-launched missiles, and mobile missiles—long Russia’s forte. This is even more alarming given Moscow’s rich tradition of cheating on treaties.

In reality, the fatally flawed pact is being rushed to obscure the failure of President Obama’s “reset” policy with Russia and a string of other national security flops.

Mr. Obama’s disavowal of George W. Bush’s foreign policy, which initially attempted to check Russia’s bullying of its neighbors, was supposed to get us something in return from Moscow. Less interference with our mission in Afghanistan would have been a nice start. Yet despite an agreement last year to ship non-lethal goods through Russia to Afghanistan, Moscow continues its general non-cooperation and is doing its best to kick the U.S. out of Central Asia. Mr. Obama hopes the pageantry of another agreement would be mistaken for real progress with Moscow.

Rather than accept a treaty as flawed as this, it would be far better for the U.S. to make Russia and other adversaries, like North Korea, believe their nuclear arsenals are of limited use, and thus not worth maintaining.

The way to do that is for the U.S. to possess a modern and reliable nuclear arsenal. Another key element would be improving systems to shoot down enemy missiles.

Unfortunately, the U.S. is stumbling. The last time America tested a nuclear warhead was in 1992. Would you defend your home and family with ammunition that has not been tested in two decades—and might be decades older still? Such is the case with our nuclear defense.

Worse, many of the same precincts of the foreign policy establishment that advocate START also want the U.S. to agree to ban all nuclear tests permanently. The high priests of arms control seem unfazed by an expected Iranian nuclear breakout and consistent nuclear progress by North Korea.

When all of these trends are combined with President Obama’s naive talk of abolishing nuclear weapons, it may cause rogue regimes and other adversaries to believe one day that the U.S. will not or cannot use nuclear weapons when necessary. Of the many dangers to which the Obama administration has exposed America, this may be the gravest yet.

The Senate should kill the START treaty and tell the Obama administration to start over and drive a harder bargain with Moscow. Our defense against nuclear assault should be based less on hope and more on reality.

Christian Whiton is a former U.S. State Department senior adviser and is a principal at D.C International Advisory. He is a frequent contributor to Fox News Opinion.