"The president believes that the interest of the United States were well served by our policy of rebalancing our attention to Asia", said White House press secretary Josh Earnest at his daily news conference.
Obama says the agreement is the product of years of work between Iran and six world powers, not just between the USA and Iran.
President Obama has previously said he is taking the first lady on a vacation to a "warm" location.
Ms Obama described moving into the White House as a "whirlwind" and took time to really settle in.
Obama also discussed Trump's unconventional political style.
The 44th president ended his message on a positive note, saying: "Eight years later, I am even more optimistic about our country's promise".
"The fact is this would have fallen through on a number of the president's promises, including renegotiating NAFTA in a way that has positive benefits for the United States economy, for American businesses and for American workers", Earnest said.
"I would have, I think, made a bigger mistake if I had said, 'Eh, chemical weapons".
Elsewhere, Obama reflected on his own shortcomings as president.
For comparison, President Obama's handling of his transition was approved by 83 percent of Americans, while 12 percent disapproved.
"I'll never forget being here after my inauguration, starting my new job and moving our family into a new home on the same day". Obama noted that he'd seen the "new place", which is temporary, and that "it's not insane big, but there's enough room for, you know, a treadmill and some workout equipment in the basement".