In 2005, American liberals achieved one of their most significant political victories of the last decade. It occurred with the resounding rejection of George W Bush's campaign to privatise social security.

Bush's scheme would have gutted the crux of that entitlement programme by converting it from what it has been since the 1940s – a universal guarantor of minimally decent living conditions for America's elderly – into a Wall Street casino and bonanza.

Progressive activists and bloggers relentlessly attacked both the plan and underlying premises (the myth that social security faces a "crisis"), spawning nationwide opposition. Only a few months after he unveiled his scheme to great fanfare, Bush was forced to sheepishly withdraw it, a defeat he described as his biggest failure.

That victory established an important political fact. While there are very few unifying principles for the Democratic party, one (arguably the primary one) is a steadfast defence of basic entitlement programs for the poor and elderly – social security, Medicare and Medicaid – from the wealthy, corporatised factions that have long targeted them for cuts.

But in 2009, clear signs emerged that President Obama was eager to achieve what his right-predecessor could not: cut social security. Before he was even inaugurated, Obama echoed the right's manipulative rhetorical tactic: that (along with Medicare) the programme was in crisis and producing "red ink as far as the eye can see." President-elect Obama thus vowed that these crown jewels of his party since the New Deal would be, as Politico reported, a "central part" of his efforts to reduce the deficit.

The next month, his top economic adviser, the Wall Street-friendly Larry Summers, also vowed specific benefit cuts to Time magazine. He then stacked his "deficit commission" with long-time advocates of social security cuts.

Many progressives, ebullient over the election of a Democratic president, chose to ignore these preliminary signs, unwilling to believe that their own party's leader was as devoted as he claimed to attacking the social safety net. But some were more realistic. The popular liberal blogger and economist Duncan "Atrios" Black, who was one of the leaders of the campaign against Bush's privatisation scheme, vowed in response to these early reports:

The left ... will create an epic 360-degree shitstorm if Obama and the Dems decide that cutting social security benefits is a good idea.

Fast forward to 2011: it is now beyond dispute that President Obama not only favours, but is the leading force in Washington pushing for, serious benefit cuts to both social security and Medicare.

This week, even as GOP leaders offered schemes to raise the debt ceiling with no cuts, the White House expressed support for the Senate's so-called "gang of six" plan that includes substantial cuts in those programmes.

The same Democratic president who supported the transfer of $700bn to bail out Wall Street banks, who earlier this year signed an extension of Bush's massive tax cuts for the wealthy, and who has escalated America's bankruptcy-inducing posture of Endless War, is now trying to reduce the debt by cutting benefits for America's most vulnerable – at the exact time that economic insecurity and income inequality are at all-time highs.

Where is the "epic shitstorm" from the left which Black predicted? With a few exceptions – the liberal blog FiredogLake has assembled 50,000 Obama supporters vowing to withhold re-election support if he follows through, and a few other groups have begun organising as well – it's nowhere to be found.

Therein lies one of the most enduring attributes of Obama's legacy: in many crucial areas, he has done more to subvert and weaken the left's political agenda than a GOP president could have dreamed of achieving. So potent, so overarching, are tribal loyalties in American politics that partisans will support, or at least tolerate, any and all policies their party's leader endorses – even if those policies are ones they long claimed to loathe.

This dynamic has repeatedly emerged in numerous contexts. Obama has continued Bush/Cheney terrorism policies – once viciously denounced by Democrats – of indefinite detention, renditions, secret prisons by proxy, and sweeping secrecy doctrines.

He has gone further than his predecessor by waging an unprecedented war on whistleblowers, seizing the power to assassinate U.S. citizens without due process far from any battlefield, massively escalating drone attacks in multiple nations, and asserting the authority to unilaterally prosecute a war (in Libya) even in defiance of a Congressional vote against authorising the war.

And now he is devoting all of his presidential power to cutting the entitlement programmes that have been the defining hallmark of the Democratic party since Franklin Roosevelt's New Deal. The silence from progressive partisans is defeaning – and depressing, though sadly predictable.

The nature of American politics is that once a policy is removed from the partisan wars – once it is adopted by the leadership of both parties – it is removed from mainstream debate and fortified as bipartisan consensus. That is why false claims in the run-up to the Iraq war, endorsed by both parties, received so little mainstream journalistic scrutiny. And it's why the former Bush lawyer and right-wing ideologue Jack Goldsmith – back in May 2009 – celebrated in The New Republic the fact that Obama was doing more to strengthen Bush/Cheney terrorism policies than his former bosses could have ever achieved: by embracing the very terrorism approach he once denounced, Obama was converting it from rightwing radicalism into into the official dogma of both parties, and forcing his supporters to defend what were, until 2009, the symbols of rightwing evil.

Identically, Obama is now on the verge of injecting what until recently was the politically toxic and unattainable dream of Wall Street and the American right – attacks on the nation's social safety net – into the heart and soul of the Democratic party's platform. Those progressives who are guided more by party loyalty than actual belief will seamlessly transform from virulent opponents of such cuts into their primary defenders.

And thus will Obama succeed – yet again – in gutting not only core Democratic policies, but also the identity and power of the American Left.