There are few more skilled anthropologists of the various tribes of American political life than Stan Greenberg.

Ever since his research in the 1980s identified the “Reagan Democrats” — white working-class voters whose abandonment of their traditional allegiance helped deliver the Republicans a string of presidential election victories — the veteran Jewish pollster has had his finger very much on the pulse of “Middle America”.

And now, as Joe Biden marks his 100th day in office, Greenberg has begun to unearth a new phenomenon. “Biden Republicans”, he argues, helped to deliver the president’s victory last November and could become “pivotal to the future of the two parties”. Among their number are two distinct groups which the president has sought to detach from their Republican moorings: affluent, college-educated, suburban voters and less well-off, Midwestern blue-collar workers whose anger at globalisation helped to seal Hillary Clinton’s fate in 2016. This latter group, believes Greenberg, saw the Democrats as “aligned with the metropolitan elites and not battling for the working-class”. He argues that “Biden has been very focused on reaching out to those voters”.

The welter of government activism that Biden has unleashed since entering the White House — last month he signed a nearly $2tn covid relief package and he now wants to spend another $2tn on infrastructure — does not surprise Greenberg and he dismisses the notion that the president’s mandate is too thin for such radical change.

“We were coming out of a pandemic, we have a deep economic and health crisis,” he says. “People wanted government to be effective. I think Trump might have gotten re-elected had he used government in an effective way but he was incapable of doing it.”

He compares the moment to 1933 when Franklin Roosevelt took office in the depths of the Great Depression. Biden, Greenberg argues, isn’t “very ideological but he does have a sense of history and what is possible”. He’s proving, he believes, “a very effective president whose taking that mandate in a very big way”.

Greenberg, who has advised a slew of centre-left politicians including Bill Clinton and Tony Blair, admits that Trump’s ability to drive-up turnout among his base “worked better than I would have expected”, producing a closer race than many had predicted last November. The former president’s campaign was “very smart and agile and ugly”, he suggests, in shifting its focus amid last year’s Black Lives Matter protests from immigration to “stirring up the black-white divide and racial hostilities”.

Race, Greenberg argues, is now “deeply embedded into the Trump project and the people that are animated by Trump.”

Focus groups he recently conducted among voters who remain loyal to the former president also suggest that antisemitism is implanted in this noxious mix. When he asked participants to write messages to Biden, one offered the words: “Don’t let the Jews control you.” The research found sympathy for the far-right, antisemitic Q-Anon conspiracy theory. Rhetoric focused on “Jews of the East Coast” and “big Jewish money” is a “big part of the narrative,” Greenberg believes.

But the message which sustained Trump’s 2020 campaign — “keep him as president, keep the deep state, keep Jewish money and keep the Democratic socialists liberals from gaining power” — has lost much of its momentum since his defeat last November. “Once you’ve lost, the narrative is actually disempowering, it makes you feel … less engaged,” Greenberg argues.

This sense of powerlessness among Trump loyalists has been compounded by the former president’s argument that the election was stolen from them thanks to Democrat skulduggery and the “weak-kneed” response to it of the Republican establishment.

While his voters currently appear despondent with politics and disengaged from it, Greenberg says he has learned not to underestimate Trump and his ability to successfully utilise racial and cultural issues.

Nonetheless, he believes Biden’s prospects over the next two years are good and hints the Democrats may defy historical precedents by holding on to their narrow majorities in the House of Representatives and Senate next November. He points to a robust economy, rising wages and, if it passes, a boost to jobs from Biden’s infrastructure plan.

For years, two-thirds of Americans have told pollsters they believe the country is on the wrong track. “Now the majority is saying we’re on the right track,” Greenberg suggests. “It’s a unique moment.”