(Bloomberg) -- President Barack Obama’s surprise call to expandSocial Security highlights a populistshift in the U.S. political landscape that has been propelled bythe campaign of Vermont Senator Bernie Sanders.

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Just five years ago, Obama called for reducing future SocialSecurity benefits -- an idea that at the time was in vogue for manyRepublicans and some Democrats, who treated it as a badge of fiscalresponsibility.

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No more.

Donald Trump, the presumptive Republican presidential nominee,says Social Security benefits shouldn’t be cut -- a departure fromother Republican leaders such as House Speaker Paul Ryan ofWisconsin.

Sanders, as part of his Democratic presidential campaign, hasbeen calling for an expansion of benefits, and the party’s likelynominee, Hillary Clinton, took a similar position earlier thisyear. Obama joined the chorus on Wednesday.

"It is a much different universe today," said Warren Gunnels,policy director for the Sanders campaign. "Go back to 2011, whenthe debate was not whether Social Security would be cut, but howmuch it would be cut. Now the debate is not whether we’re going toexpand Social Security but how much we’ll expand it."

Five years ago, Obama offered to change the way Social Securitybenefits are calculated to make them less generous as part of a"grand bargain" on taxes and spending with then-House Speaker JohnBoehner, an Ohio Republican. He officially abandoned the policy inhis fiscal 2015 budget, then went further in a speech in Indiana onWednesday in which he excoriated Republican economic policies andcalled for Social Security benefits to be expanded.

Obama never supported Social Security cuts and would only agreeas part of a larger deal with Republicans, Josh Earnest, the WhiteHouse press secretary, said on Thursday. It was included in Obama’sbudget "to illustrate what impact that could have on our fiscalsituation, but only as a larger part of a so-called grand bargain,"Earnest said.

Sanders’s ‘snowball’

Obama’s change of heart reflects changes in both the economy andpolitics. Budget deficits have plunged since 2012, reducingpressure to cut entitlement spending. A 2014 Federal Reserve surveypublished last year found that 42 percent of American workersearning under $40,000 a year, and a quarter earning between $40,000and $100,000, have no retirement savings. Years of partisan warfarehave meanwhile killed appetite in both parties for painfulpolitical compromises.

Though Sanders is unlikely to win the Democratic presidentialnomination, the emerging orthodoxy of his party calling for anexpansion of Social Security owes as much to him as anyone.

In March 2015, as the top Democrat on the Senate BudgetCommittee, Sanders pushed for a vote on an amendment byMassachusetts Senator Elizabeth Warren proposing expanded SocialSecurity benefits. Forty-two Democrats voted for the amendment andonly two were opposed.

"That certainly was a very significant moment," Gunnels said ofthe budget vote. "It really has been a drumbeat and a snowballthat’s gotten much larger through the Sanders campaign and throughthese many years of grassroots efforts."

Two months later, when Sanders announced his presidential bid,he put the policy front and center. "Instead of cutting SocialSecurity," he said, "we’re going to expand Social Securitybenefits."

In February, after months of pressure from Sanders and liberalsin her party, Clinton followed his lead. "I won’t cut SocialSecurity," she said on Twitter. "As always, I’ll defend it, &I’ll expand it."

Obama jumped aboard, unifying the party’s leadership behind thepolicy.

"It is time we finally made Social Security more generous andincrease the benefits," he said, "so that today’s retirees andfuture generations get the dignified retirement that they haveearned."

‘Political calculation’

Conservatives still wedded to the idea of cutting the programalso credit Sanders.

"The Bernie Sanders campaign, from the free love generation tothe free everything generation, has pushed everybody left. And thepresident’s gone right along with him," said Doug Holtz-Eakin, aformer director of the Congressional Budget Office who now leadsthe American Action Forum, a conservative advocacy group.

Endorsing expansion represents a "crass political calculation"by Obama, he said. Liberals were indeed overjoyed by Obama’sremarks, and his endorsement of a policy championed by Sanders mayhelp unify his party after a divisive primary campaign.

"The program is not sustainable in its current form,"Holtz-Eakin said. "Adding more benefits doesn’t do anything to helpthat."

While the Baby Boomer generation is expected to strain SocialSecurity, the program is running a surplus and will have enoughreserves in its current form to dole out full benefits until 2034,according to the 2015 report from its trustees.

Leftward shift

Norm Ornstein, a scholar at the American Enterprise Institute inWashington, attributes the political shift leftward to twodevelopments. First, the federal budget deficit has been nearlyhalved since 2011, from $1.3 trillion to a projected $544 billionin 2016, according to the Congressional Budget Office, reflectingimprovements in the economy.

"As soon as the short-term deficits came down, interest indealing with the long-term problem sort of evaporated," saidWilliam Gale, director of the Brookings Institution’s RetirementSecurity Project and a former staff economist for RepublicanPresident George H.W. Bush’s Council of Economic Advisers.

Second, Obama’s overtures to strike a deficit-reduction dealwith Republicans were rebuffed in 2011 and again in 2013, leadinghim to be "more adventuresome" with his policies, Ornsteinsaid.

The deal Republicans could have struck in 2011 "was anunbelievable deal politically for them," Ornstein said. But becausethey would not consent to tax increases, the talks went nowhere, hesaid.

In the months after Obama’s re-election, he extended Republicansan olive branch by including in his budget a proposal to reduce thegrowth of Social Security benefits by indexing them to a lower rateof inflation. After Republicans again spurned his overtures in2013, Obama abandoned the proposal.

"It was time to go on offense," said Mike Darner, the executivedirector of the Congressional Progressive Caucus, which proposed aSocial Security expansion ahead of the 2012 election. "It’s anissue that was ripe for this moment in time."

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