In the movie “Kramer vs. Kramer” a father struggles to discipline his young son, who knows from experience that all warnings about consequences for his bad behavior are empty ones. The son gets up in the middle of dinner to get the ice cream from the freezer knowing that nothing ever happens when he simply disregards what is said to him.

Thus “You go right back and put that back” becomes “I’m warning you, you take one bite out of that and you are in big trouble,” which becomes “Don’t you dare go anywhere beyond that,” which becomes “I am not going to say it again.”

This calls to mind President Obama’s most recent threat to veto a U.S. Senate bill with bipartisan support aimed at incentivizing Iran to end diplomatically the international threat posed by its pursuit of nuclear weapons. The bill, introduced by Sens. Robert Menendez (D-N.J.) and Mark Kirk (R-Ill.), provides for further sanctions if, after yet another six months of negotiations, Iran still refuses to reverse its nuclear program, as it has steadfastly refused to do over the course of the last year. It enables the president to waive these sanctions, as long as he certifies that continuing the talks “is likely to result in achieving a long-term comprehensive solution with Iran.”

Over the past year, the Obama administration has eased sanctions on Iran and repeatedly threatened to veto legislation that would reinstitute the sanctions if Iran continues to refuse a nuclear deal, at times accusing the bill’s supporters of wanting a war. While giving the president a full year of the “space” he said he needed to negotiate has produced no agreement, the easing of sanctions has handed Iran significant improvements in its economy, thereby reducing any pressure Iran may have felt to make a deal.

It was Obama who derided the idea of sanctions on Iran as “Bush-Lite” during the 2008 presidential campaign, and who sought to block Congress from enacting sanctions after he was elected. He now acknowledges that it was the very sanctions he opposed that are responsible for persuading Iran to negotiate — but he makes the head-scratching argument that if Iran knows the sanctions will be strengthened if it continues to dither, it will break off negotiations.

With senators on both sides of the aisle supporting the Menendez-Kirk bill, Obama hopes he can keep it from collecting the 67 votes necessary to make it veto-proof. In this he relies on Democratic senators to oppose the bill not because they disagree with it, but because he has asked them to.

One promising candidate for Obama is Massachusetts US Sen. Ed Markey. Those who have followed Markey can recite by heart his claims to have been ahead of his time on the dangers of nuclear proliferation, or his applause line about stopping Iranian nuclear designs by squeezing Iranian leaders with sanctions so tight “that their eyes will bulge out of their sockets.” When an earlier version of the bill was introduced last year, however, Markey declared that he could not support it because the White House had asked him not to.

This is the same Ed Markey who won election to Congress in 1976 by trumpeting his independence from his Democratic leaders in the Massachusetts Legislature, who had moved his desk into the hallway in pique. “They may tell me where to sit,” he intoned in the television spot credited with securing his election, “but nobody tells me where to stand.”

With the specter of a nuclear Iran terrifyingly real, Markey and his colleagues ought to remember what they themselves have said in the past. If they oppose Menendez-Kirk they will send the message to Iran that it may do as it pleases, without consequences.

This piece was published previously in The Boston Herald