WASHINGTON -- Not so long ago, a bad week for U.S. President Barack Obama was one that sparked comparisons to Jimmy Carter, a popular whipping boy for the right who was considered weak and ineffectual by many Americans.

Seven months into his second term, and the Carter comparisons are a distant memory: now Obama's being likened to former presidents Richard Nixon and George W. Bush, popular targets for the commander-in-chief's liberal base.

Revelations about the Obama administration's sweeping surveillance practices, as well as the ongoing investigation into the IRS's targeting of Tea Party organizations, have resulted in a litany of comparisons to both former presidents in recent weeks.

Edward Snowden himself, a libertarian who donated to Ron Paul's presidential campaign in 2012, made the comparison in explaining why he leaked details of two top-secret U.S. government surveillance programs to two news organizations last week.

"I believed in Obama's promises," Snowden told Britain's The Guardian. "He continued with the policies of his predecessor. I do not want to live in a world where everything I do and say is recorded."

For the second day running, White House press secretary Jay Carney spent much of Tuesday's daily news briefing denying Obama has expanded some of the most troubling surveillance practices of the Bush administration, most of them springing from the traumatic aftermath of the terrorist attacks of Sept. 11, 2001.

"It's important ... to be fully aware of the kind of oversight that exists when it comes to these programs," Carney said, reiterating his insistence that Obama has added significant safeguards to Bush-era practices.

A day earlier, Carney was more forceful in pointing out the contrasts between Obama and his predecessor.

"In every case, this president's policy has been different," he said.

"The president's record on making the kinds of changes that he promised he would make to the ways that we pursue our fight against al-Qaida and our fight against terrorists and extremists, he has lived up to."

But the comparisons are gaining steam with the help of social media. A photographic mash-up of the two men, first appearing on the Huffington Post, has gone viral this week. The moniker "George W. Obama" has also cropped up in news headlines and on Twitter.

New York Times columnist Maureen Dowd wrote that Obama could no longer be referred to as "Bush-Cheney Lite" because there was nothing "lite" about the Bush-era surveillance practices embraced, and in some cases expanded, by his administration.

There was some good-natured ridicule, too, with the birth of a blog called Obama Checking Your Email. It's a series of photos of a cheerful Obama gazing at various computer screens while on presidential outings.

The Nixon comparisons, meantime, have been levelled by those who argue the IRS controversy is on par with Watergate, the infamous wiretapping scandal that resulted in the president's resignation in 1974. In addition to the wiretapping, Nixon also ordered the IRS to go after his political enemies.

Senate minority leader Mitch McConnell has made the comparison, as have conservative commentators that include George Will. Obama himself was even asked about the comparison by a reporter at a recent Rose Garden news conference.

"I'll let you guys engage in those comparisons," Obama replied. "You can go ahead and read the history, I think, and draw your own conclusions."

But one famous Watergate figure recently scoffed at attempts to compare the IRS controversy to Watergate.

"It is certainly not Watergate, and it is certainly not Nixonian activity," said John Dean, Nixon's White House counsel.

"It's a scandal, it just doesn't reach very high -- it's a scandal within the IRS," he said. "It's been drummed up. There's no question what IRS did was wrong, but there's no evidence that there was any activity outside the IRS."

Stephen Hess, a one-time political aide who worked for both Nixon and Dwight D. Eisenhower, agreed that there are no comparisons to be made between Obama and Nixon.

"There are no similarities to Watergate or Nixon at all," said Hess, now a senior fellow at the Brookings Institution think-tank in D.C.

"Watergate was an election scandal, one that had to do with a president protecting his political turf. On the surveillance scandal, this is a long series of events, including laws and regulations, beginning after 9-11 and moving forward with the blessing of both parties in order to protect national security."

The IRS controversy, meantime, "barely touches what Nixon was up to," Hess said.

Obama's presidential legacy is not at risk from either controversy, said Cal Jillson, a political science professor at Southern Methodist University in Dallas.

It's meaningful legislation that largely determines a presidential legacy, not "distractions," Jillson said.

"The key thing on the table in Obama's second term is the immigration bill," he said.

"If that gets through, it will be a huge signature piece of legislation for Obama, similar to health care reform in his first term. And it would result in substantive policies that would impact people's lives in a significant way."

The scandals, meantime, are something of a tempest in a teapot, Jillson said.

"There is nothing that is anywhere near being impeachable offences, let alone criminal. They won't result in a single charge against the administration other than political arrogance."