"It is incumbent on the critics of this deal to explain how an American president is in a worse position -- 12, 13, 14, 15 years from now -- if, in fact, at that point, Iran says, 'We're going to back out of the (deal), kick out inspectors, and go for a nuclear bomb,'" he said at an afternoon press conference.
Obama spoke for more than an hour Wednesday, taking questions from reporters, but shifting to posing some questions for himself at the end of the press conference, apparently looking to draw out his critics.
Throughout the event, Obama told reporters the chief goal in the negotiations was to ensure Iran cannot construct a nuclear bomb.
"This deal is our best means of ensuring Iran does not get a nuclear weapon," he said.
Obama also hit back against critics who said that international inspectors would not have instant access to nuclear sites anywhere in the country, a contention that has caught fire in the hours since the deal was unveiled Tuesday morning.
The President said the deal established thorough monitoring "24-7" and that Iranians cannot simply sneak nuclear fuel past inspectors.
"This is not something you hide in a closet. This is not something you put on a dolly and wheel off somewhere," Obama said of enriched uranium and plutonium.
Obama was talking directly with the press, but his real audience was skeptical Democrats
on Capitol Hill, who could join with Republicans to scuttle the deal.
"My hope is that building on this deal, we could continue to have conversations with Iran that incentivize them to behave differently in the region," Obama said.
White House officials have been trumpeting the measure for the limits placed on uranium enrichment and broad access for international inspectors.
But Republicans have panned the measure as caving to Iran. And Israeli Prime Minister Benjamin Netanyahu, who holds bipartisan sway in Washington, has called it a "historic mistake."
Sen. Tom Cotton, R-Arkansas, told CNN's "New Day" Wednesday morning that after reading through the deal, he had determined "it's not as bad as I feared, it's actually much worse."
But Obama said Wednesday that "I am not betting on the Republican Party rallying behind this agreement."
Democratic frontrunner and former Secretary of State Hillary Clinton plied legislative Democrats on Tuesday during private meetings on the Hill.
Obama warned Tuesday that he would veto any congressional measure that throws the deal off track -- effectively pushing the bar for Republicans and Democratic opponents to the two-thirds majority needed to override a veto.