A steely Obama travelled to Pittsburgh, Pennsylvania where he urged the 1.9 million member Veterans of Foreign Wars to give the nuclear deal with Tehran a chance.
He denounced those "chest beating" against the deal and said some of those opposed to it were the same ones who said the Iraq war would take months.
"We know the consequences of that choice," he said. "And what it cost us in blood and treasure.
Insisting he was no peacenik afraid to deploy the military, Obama boasted about a string of military operations that took high-ranking Al-Qaeda officials -- including Osama bin Laden -- off the battlefield.
More From This Section
"If you target Americans you will have no safe haven," he said.
But, he added, "real leadership" means not being afraid to negotiate.
Obama has framed the recent nuclear deal as a choice between diplomacy and war.
While campaigning for the presidency in 2008, Obama told a battle-weary nation he would end the long and bloody conflict in Iraq as president made winding down the wars there and Afghanistan a priority.
Today, the Obama administration rolled out a Twitter feed and website that White House spokesman Josh Earnest said will be used to "distribute facts, engage online audiences and be used as a forum by those involved in negotiating the agreement."
Obama also paid tribute to five US troops killed in Chattanooga, Tennessee after an attack Thursday on two military centers by a 24-year-old gunman, Mohammad Youssuf Abdulazeez.