"This is such an important decision that I will not let pressure, politics or party influence," said Schumer, the No. 3 Senate Democrat who is poised to take over as Senate Democratic leader in 2016 and is considered one of the most critical votes on the Iran deal. "I have learned over the years that when you have a tough decision like this: study it, come to what you believe is the right decision and go forward with it. And that's what I intend to do."
The agreement is staunchly opposed by Republicans and may earn a nod of disapproval from some Democrats. How Schumer votes could influence others in his party, and he is coming under intense lobbying from the Obama administration to support the deal and from outside groups to oppose it.
President Barack Obama has to have enough Democrats supporting the deal to prevent opponents from reaching a veto-proof majority in the Senate.
"This is one of the most important decisions that I'll make," Schumer said Monday at a press conference on an unrelated topic, noting that he's had over 20 briefings on the matter, including two classified briefings.
"I intend to continue that because this is such an important decision," Schumer said. "I am studying it extremely carefully."
Schumer declined to say with whom he's discussed the deal, but noted that both the White House and people opposed to the deal are "making every effort to answer my questions."
Schumer was among the dozen plus Democratic senators who joined Republicans to pass Tennessee Republican Sen. Bob Corker's bill that ensured the Iran deal will need to face a congressional vote.
While Schumer said he was still studying the merits of the deal, two other Democrats announced Monday that they had made up their minds.
A fellow New York Democrat, Rep. Kathleen Rice, said Monday that she will vote to oppose the deal, calling it "a pause, not an end, to Iran's quest for a nuclear weapon."
Meanwhile, Rep. Adam Schiff, the top Democrat on the House intelligence committee, voiced support Monday for the agreement.
"The deal realistically precludes Iran from developing an atomic bomb for fifteen or more years, and does so while reducing the chances of war," he said in a statement calling the deal "a major achievement."