"Right now, the opponents of this deal have been flooding congressional offices. There are 20 million ads up right now in districts to put pressure on members of Congress. And they are feeling it," Obama said on a conference call with grassroots supporters. "I'm meeting with the members of Congress and they don't really buy the arguments of the opponents but I can tell when they start getting squishy and they start getting squishy because they are feeling the political heat."
The blunt assessment comes as members of Congress head back into their districts for the month of August, and could face contentious town halls with their constituents.
On the conference call were a plethora of progressive organizations and the coalition that carried over from his 2008 and 2012 campaigns, like Obama For America, MoveOn and Americans United for Change, among many others.
The President turned the call into something of a call to arms ahead of those town halls, telling his supporters to "get loud and active" against the other side's lobbying effort. He warned them that without their voices, he believes, the same forces that got the U.S. into the Iraq War could scuttle this deal.
"The lobbying that is taking place on the other side is fierce, it is well financed, it is relentless. And in the absence of your voices, you are going to see the same array of forces that got us into the Iraq War, leading to a situation in which we forgo a historic opportunity and we are back on the path of potential military conflict."
"If you've got a whole bunch of folks who are big check writers to political campaigns, running TV ads and billionaires who happily finance super PACs and they are putting the squeeze on members of Congress, even well-meaning ones and good folks, and they don't hear from you, this opportunity can slip away," he added.
Obama warns House Democrats
The conference call follows a warning from Obama to House Democrats on Wednesday night not to reject the nuclear deal.
According to two House Democrats who attended a reception at the White House with the President, he predicted there would be fallout for future relationships abroad if Congress failed to back the agreement with Iran at the end of a 60-day review period in September.
New York Democratic Rep. Jerry Nadler summarized the president's message, saying he told House Democrats that if they helped block the deal, "It's going to greatly lessen our credibility in dealing with anything in the future because people are going to say for a long time: 'You can't deal with them because who knows what they're going to do.'"
Nadler met one-on-one with the President before the entire House Democratic caucus heard a 20-minute presentation by Obama on the details of the deal. Rep. Eliot Engel of New York, the top Democrat on the House Foreign Affairs Committee who has been skeptical of the Iran deal, also had a one-on-one meeting with Obama.
With no time for questions after the meeting was disrupted by votes, White House Press Secretary Josh Earnest said that the President invited any member who had questions to come back. A couple dozen took him up on the offer, so after votes were completed that group returned to the White House and spent nearly two hours with the President.
Earnest described the conversation with House Democrats as "taking on directly some of the most common criticism of the agreement" and also noted his interest in having one-on-one meetings.
"Spending time with individual members of Congress and answering their questions directly, again, I think is an indication that the president feels a personal responsibility to engage with members of Congress who are keeping an open mind," he said.
Earnest said the President will continue to have many other conversations like these over the next several weeks. He disputed the notion that there is a "sense of urgency" right now due to concerns, but rather said it is because many members of Congress are leaving town over the next few weeks so the President want to sit down and talk with many of them before they left.
Following the discussion, Nadler said he's still wrestling with the decision of how he'll vote on the deal and the arguments Obama made.
"His message is that this is important, that if we want to avert a nuclear bomb in Iranian hands, we have to vote yes for this, there's no other way. There are no other alternatives that bear close scrutiny," he said.
Nadler said the President "makes an impressive case" but that he still has questions.
A CNN/ORC poll this week
found that a majority of Americans want Congress to reject the nuclear deal with Iran. Overall, 52% say Congress should reject the deal, 44% say it should be approved.