The CNN/ORC International survey, released Monday, finds that Obama's approval rating has fallen eight points to 45 per cent, the lowest level in more than 18 months. A slim majority of respondents also said they found Obama untrustworthy for the first time in his presidency.
Among people under 30, African-Americans and independents, the poll shows a 17 percentage point drop in support for the president.
The survey, conducted after news broke about the National Security Agency's counter-terrorism surveillance practices, was released as former government employee Edward Snowden answered questions about his decision to leak details of the far-reaching email and phone-log monitoring programs to the media.
"I did not reveal any U.S. operations against legitimate military targets," Snowden said in a live chat on the website of Britain's The Guardian newspaper.
"I pointed out where the NSA has hacked civilian infrastructure such as universities, hospitals and private businesses because it is dangerous. These nakedly, aggressively criminal acts are wrong no matter the target."
He assailed congressional leaders — and former vice-president Dick Cheney — for calling him a traitor.
"Being called a traitor by Dick Cheney is the highest honour you can give an American, and the more panicked talk we hear from people like him ... the better off we all are," said Snowden, thought to still be in hiding in Hong Kong.
"This is a man who gave us the warrantless wiretapping scheme as a kind of atrocity warm-up on the way to deceitfully engineering a conflict that has killed over 4,400 and maimed nearly 32,000 Americans, as well as leaving over 100,000 Iraqis dead."
Snowden said he won't be silenced.
"The U.S. government is not going to be able to cover this up by jailing or murdering me," he said, adding he will not return to his native land voluntarily since the government has "immediately and predictably destroyed any possibility of a fair trial at home."
The surveillance scandal is just one among several plaguing the Obama administration in recent weeks. But until the NSA leaks, Obama's approval ratings remained relatively steady despite news that the IRS had targeted Tea Party non-profit organizations and the U.S. Justice Department had seized the phone records of journalists while investigating national security leaks.
"The drop in Obama's support is fuelled by a dramatic 17-point decline over the past month among people under 30, who, along with black Americans, had been the most loyal part of the Obama coalition," Keating Holland, CNN's polling director, said in a news release.
"It is clear that revelations about NSA surveillance programs have damaged Obama's standing with the public, although older controversies like the IRS matter may have begun to take their toll as well."
Since the NSA story broke, 50 per cent of Americans do not think the president is "honest and trustworthy," according to the CNN poll, while 49 per cent do. That's the biggest show of distrust in the president since he won the White House in 2008.
The survey also found that even though most Americans support the surveillance programs if they're focused on Internet communications with those living abroad, 62 per cent said they felt the government has become so "large and powerful that it poses an immediate threat to the rights and freedoms of ordinary citizens."
Sixty-one per cent gave Obama a thumbs-down in terms of how he's handling surveillance; only 52 per cent disapproved of George W. Bush's surveillance practices.