With its relentless quest for nuclear weapons, the Iranian regime represents a serious and growing threat to our national security. Sadly, our nation's ability to counter that very threat is being hamstrung by another problem - President Barack Obama's sheer desperation for a legacy foreign-policy achievement. The unfortunate result is that Iran may soon be handed a highly advantageous deal, putting it closer than ever to its ultimate goal of a nuclear bomb.

The United States has no bigger or more dangerous adversary in the Middle East than the radical regime in Tehran, led by the so-called Supreme Leader. Iran has attacked Americans and undermined our national interests for the last 30 years, ranging from the 1983 Iran-sponsored terrorist attacks on the U.S. Embassy and Marine barracks in Lebanon to the Iran-sponsored roadside bomb attacks on American troops in Iraq during the latter years of the Iraq war. Iran has the blood of hundreds of Americans on its hands, and that must be foremost in our minds as context when we deal with Iran on any issue of national security, including the P5 plus 1 negotiations. The very premise of negotiating in good faith with such a rogue regime - the foremost state sponsor of terrorism on the planet - is pure fantasy, especially when it comes to nuclear weapons.

Even if you can set aside that skepticism long enough to assess the merits of the emerging deal, the magnitude of the president's reported concessions to Tehran is breathtaking, as are its implications. His emerging deal would preserve a robust Iranian infrastructure for enriching uranium for the next 10 years, keeping the mullahs right on the front doorstep of the nuclear weapons club and implicitly recognizing their right to enrich. After the 10-year deal expires, all bets are off, and Iran would be within short reach of a bomb. The president's deal also ignores Iran's shadowy ballistic missile program and would do little to restrict Iran's plutonium track for acquiring a nuclear weapon.

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Even if the terms of this deal were perfect, it would still have a fatal flaw: It requires us to assume good-faith disclosure on the part of a regime that has in the past lied and deceived regarding its nuclear program as a matter of standard practice. We are supposed to trust that the world's foremost state sponsor of terror is not hiding any underground enrichment bunkers or other nuclear facilities or squirreling away unknown inventories of centrifuges, uranium or other nuclear materials? That is a lot to ask.

In essence, the emerging deal would jettison the longstanding U.S. policy of preventing a nuclear-armed Iran in favor of a feeble 10-year containment plan that will basically cement Iran's status as a nuclear-threshold nation. In other words, accepting this deal would mean resigning ourselves to the fact that Iran will have the bomb one day. I simply refuse to do that. Such an outcome would be terribly dangerous for the Texans I represent.

The White House says opponents of this deal are simply in a "rush to war," which is insulting to the intelligence of Americans everywhere. There are options available other than diplomatic negotiations and war, but the president does not want you to think about those. Instead of accepting a lopsided deal that lights the path for Iran to the bomb and revives the economic engine it needs to get there, it is time to bring to bear devastating sanctions on Iran, with the credible threat of decisive American military action as a backstop and a last resort.

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In the long run, the mullahs will never abandon their nuclear weapons quest unless they believe America has the means and the will to do whatever it takes to prevent them from getting the bomb. In the short run, Congress will need to intervene to avert this very bad deal and put America's boot back on Tehran's neck. Doing so will likely necessitate overcoming Obama's veto of upcoming legislation. It is necessary for the safety of Texans and all of Americans.

Sen. John Cornyn, R-Texas, is the Senate Republican whip. Reach his office through his website, www.cornyn.senate.gov.