Senator Charles Schumer on Sunday pointed to his opposition to the Iran nuclear deal as proof that he will not serve as a rubber stamp to a possible President Hillary Clinton if elected as the Senate Majority Leader next year.

“When I disagree with Secretary Clinton, I will. She and I disagreed greatly, for instance, on the Iran agreement,” Schumer said in a TV debate with his Republican challenger, Wendy Long, aired on NY1, when asked how he will demonstrate his independence should he be in control of the chamber. “I thought that was a very bad idea. She thought it was a good idea. And that didn’t stop me; I studied it, I had lots of briefings, and I came to the right conclusion.”

“So when I think President Clinton is wrong, I will disagree with her,” he promised.

Schumer is one of seven Democrats who signed a letter to Senator Mitch McConnell asking that he “prioritize” a clean extension of the Iran Sanctions Act during the Senate’s end-of-year session. The extension, as proposed by the senior Democrats, would run through 2026. “It is essential that Congress keep Iran’s feet to the fire to make sure they do not violate the JCPOA. This bill would provide the sanction authority that helps us do just that,” Schumer said in July.

But his Republican opponent challenged Schumer for not opposing the Iran deal hard enough.

“Your behavior was very peculiar,” Long said. “You agonized over it, and then you said you finally came to this conclusion that it was a bad deal. You were right about that. But then, suddenly, you just went out of character. Because what you usually do when you come to a really intelligent conclusion is you want to stand in front an a nice podium… and tell people what was wrong with the deal. And not only that, because you’re so influential and so powerful, you want to persuade your colleagues to do the right thing. So it was puzzling to a lot of us when you didn’t want to do that given that so much is at stake and that the Iran deal was such a bad deal.”

Long added she was also puzzled that “we don’t hear a peep from you” in wake of the recent revelations on the nuclear deal.

Schumer defended the way he handled his stance on the deal, saying his failure to persuade fellow Democrats to oppose the deal was not for lack of trying, but that President Obama was more successful in whipping the votes in favor of the deal.  “I heard some people say, ‘Why don’t you twist some arms and force people to vote against it using your clout?’ That’s not how the senate works,” Schumer explained. “For me it was a decision of conscience. I had an obligation to tell people my reasoning, but go no further because for other people it was a decision of conscience too, and I respect that.”

Polls show Schumer leading Long by almost 40 points.