Those who want to maintain endless tension and animosity between the United States and Iran, and who thus have been endeavoring to kill any diplomatic agreement between the two countries, are racing ahead with their latest project and will be very busy during the week ahead. That project, the AIPAC-promoted Kirk-Menendez sanctions bill, will be the subject of a Senate banking committee hearing, with only anti-agreement witnesses so far announced, on Tuesday, to be followed by the committee's mark-up of the bill on Thursday.

Promoters of the bill are racing to beat two things. One, and worst from the promoters' point of view, would be completion of the international negotiations (which also are due to resume in plenary session this coming week) to limit Iran's nuclear program and announcement of an agreement. Even before any agreement is reached, those pushing the bill also have to worry about losing the support of those who may have originally believed the cover story that the legislation is intended to strengthen the hand of U.S. negotiators but who come to realize that the legislation is instead about spoiling the negotiations and killing a deal. Key among this group are Senate Democrats, including some who in the last Congress signed on as co-sponsors of an earlier version of the Kirk-Menendez bill.

Those in this group, and anyone else who might genuinely but mistakenly believe that passage of this bill would aid negotiations, would do well to pay close attention to the comments on this subject from British Prime Minister David Cameron, in a joint press conference with President Obama at the White House on Friday. “On Iran,” said Cameron, “we remain absolutely committed to ensuring that Iran cannot develop a nuclear weapon. The best way to achieve that now is to create the space for negotiations to succeed. We should not impose further sanctions now; that would be counterproductive and it could put at risk the valuable international unity that has been so crucial to our approach.”

The prime minister further commented on how those who had predicted that the sky would fall with the reaching 14 months ago of a preliminary agreement—which already has placed the most important restrictions on Iran's nuclear program to ensure that it stays peaceful—have been proven wrong. “To those who said,” stated Cameron, that “if you do an interim deal, if you even start discussing with the Iranians any of these things, the sanctions will fall apart, the pressure will dissipate, no one will be able to stick at it—that has demonstrably been shown not to be true.”

Some background to these remarks from the British leader are useful to keep in mind. The United Kingdom is a full participant in the nuclear negotiations with Iran, as part of the P5+1 (or EU3+3, as they prefer to say on the other side of the Atlantic). It is not an interloper in someone else's diplomatic business, and British diplomats and leaders have at least as much basis as anyone else for knowing what is working and what is not in the negotiations.

Britain also is a country that, like the United States, has historically had some really bad relations with Iran. In Britain's case this experience dates back to a British and Soviet invasion of Iran during World War II, beginning an occupation that extended until almost a year after the end of the war.

Today, the United Kingdom—unlike certain other countries that would like to influence the fate of the nuclear negotiations—has no significant interests in the Middle East that are discernibly at odds with those of the United States. And the comments on Friday came not from some soft post-conflict European liberal, but instead from the leader of the Conservative Party in the country that is still in many respects America's most important ally.

There are two major takeaways from Cameron's comments. One is to provide further confirmation that the myth that something like the sanctions bill before the Senate would facilitate negotiations and hasten an agreement is exactly that: a myth. When people actually doing the negotiating say something would weaken rather than strengthen their negotiating hand, that's a good indication that it indeed would not strengthen their hand.

Actually it should not even be necessary to get independent confirmation of this from someone like Cameron. Even if one were to assume the very worst about Barack Obama's objectives—such as that he were willing to give up the store solely to claim a foreign policy achievement or to burnish his legacy—there would be no conceivable reason for him to oppose any measure that really did strengthen his bargaining hand rather than weaken it.

The other takeaway to be had from the comments of an allied leader concerns the likely fallout if the deal-killers succeed in their effort through something like the sanctions bill. The most direct consequence would involve the responses of Iran. In the best, or least bad, case it would mean greater Iranian reluctance to make concessions because Iranian confidence in Washington's ability and willingness to live up to its end of a deal would be shaken even more than it already is. In a worse case it would mean an Iranian conclusion that the Congressional action is so counter to the spirit if not the letter of the interim agreement that the only alternative is to leave the negotiating table and go home.

But the further consequences concern the responses of the rest of the international community. Cameron indirectly reminded us of that by saying that he was commenting as “someone who played quite, I think, a strong role in getting Europe to sign up to the very tough sanctions, including oil sanctions, in the first place.” The interim agreement did not cause the beloved sanctions regime to unravel. But if the U.S. Congress wanders so far away from an international consensus and off into right field that it is seen as the main impediment to an agreement, unraveling is likely to begin.

Good, reliable allies have several uses, and not just in providing more warplanes to fight someplace. Helping to protect ourselves from our own solipsistic tendencies is another thing they can do for us.