Congressional action on Iran is a moving target. One day Democrats seem ready to pass sanctions or join with Republicans in a resolution defying the Obama administration; the next they wilt under pounding from the White House. When grilled about their about-face, they either plead “bad timing” or, as Sen. Robert Menendez’s office did yesterday, simply refuse to explain it. No wonder they don’t wish to explain themselves: Their sheepish retreat in the face of White House hysterics undermines their image as strong defenders of Israel and Congress’s role as an important actor in foreign policy.

U.S. Under Secretary of State for Political Affairs Wendy Sherman arrives prior to the start of two days of closed-door nuclear talks at the United Nations offices in Geneva Switzerland, Thursday, Nov. 7, 2013. Six world powers are dangling the prospect of easing some sanctions against Iran if Tehran agrees to curb work that could be used to make nuclear weapons. Talks resume Thursday between Iran and the six _ The United States, Russia, China, Britain, France and Germany. (AP Photo/Keystone, Martial Trezzini) Under Secretary of State for Political Affairs Wendy Sherman. (Martial Trezzini/Associated Press)

The good news for those concerned about U.S. national security is that White House pressure doesn’t last long and isn’t effective indefinitely; discussion on sanctions and congressional resolutions therefore remain active.

Long-time Democrat and pro-Israel activist Josh Block, now president of the Israel Project, observed Thursday evening, “Top Democratic and GOP leaders in the House have agreed to a [resolution] text, and the Senate continues to move forward in a bipartisan push to increase pressure on Iran and define success in any final agreement.” The question, he said, is not “if,” but “when”: “More sanctions are inevitable, it’s only a matter of timing, and that timing is dwarfed by the historic depth and breadth of public concern and the very public concerns being expressed by both Democrats and Republicans about any deal with Iran would leave the world’s leading state sponsor of terror with everything they need to build nuclear weapons.”

The Senate still may act next week before it goes on recess for the balance of the week, or — more likely — in January. Potential Senate action does three things:

First, it continues to engage the domestic and international public. Senate debate educates the public that the interim deal is a bad omen of things to come and that at least the U.S. Congress does not accept the premise that the Iranian regime should be entitled to enrich uranium. That public pressure is important not only in pressuring and electing leaders, but in extending legitimacy to actions by Israel, the Gulf states and others if military force is ultimately needed.

Second, Congress has already given the administration a scare and yesterday forced it to make the first move on sanctions in months. As the Christian Science Monitor reported, “In a move designed to convince Congress that a recent nuclear deal does not mean the US is going soft on Iran, the Obama administration on Thursday hit an additional two dozen companies and individuals with punitive measures for aiding Iran’s nuclear program. The designation – for Iranian and foreign companies and individuals found contributing to Iran’s progress in uranium enrichment and evading existing US and international sanctions – comes as the administration tries to head off mounting pressure in Congress for a new round of sanctions against Iran.”

And finally, congressional involvement acts as a spine-stiffener for the U.S. negotiators in their implementation talks with Iran. Surely the administration now understands a weak implementation deal that, for example, does not afford full access for inspectors will only trigger those sanctions.

In essence, Congress is establishing a three-sided negotiation. The United States can’t run too far in Iran’s direction or Congress will revolt, pass sanctions and potentially expose the negotiations as a façade. Unlike previously, when negotiator Wendy Sherman could construct a deal with North Korea that was obviously going to be violated, this time she has minders in the form of the U.S. senators. She should be looking over her shoulder whenever she gets the urge to acquiesce to the mullahs.