Though more than 18 months away, the 2020 presidential race is well under way in the United States.

With an unpopular Republican incumbent, the Democratic Party is attracting a huge field, with at least 10 major candidates already declared and undoubtedly more to enter in the coming months. It is an ethnically diverse field, full of women, ranging from two 37-year-olds, just old enough to run, to two candidates who will be over 70 by election day.

But as diverse as the slate of candidates is, it is relatively united in its vision for the future: one in which the federal government plays a much larger role in the economy. From Medicare for All to the Green New Deal to universal childcare, Democrats are embracing an agenda that sits significantly to the left of the party in the 1990s and 2000s.

From Medicare for All to the Green New Deal to universal childcare, Democrats are embracing an agenda that sits significantly to the left of the party in the 1990s and 2000s.

And while the new Democratic agenda in some ways reflects a return to its roots - calls for universal healthcare and a higher minimum wage were part of the party’s platform in the 1940s - it also reflects a new reality: after years of congressional inaction, the party is looking for sweeping solutions.

The Democrats’ move to the left is as much a product of polarisation as a cause of it.

Take the Green New Deal, a plan to decarbonise the American economy. Though not all Democrats support it, it has attracted significant backing from the party’s left wing, and is already reshaping the conversation around climate change legislation.

Part of the reason it has caught on is because of mounting frustration over the lack of action. With one party steeped in climate change denialism, attempts to put in place gradualist policies like carbon taxes, environmental regulation and international agreements have been abandoned.

Indeed, with the withdrawal from the Paris Agreement and the rollback of environmental protections under the Trump administration, the US has been doing less about climate change in recent years. For many Democrats, the lack of action has exacerbated the need for more comprehensive action.

The same is true for healthcare. The Affordable Care Act, passed in 2010, was a gradualist effort to attempt much-needed reforms to one of the world’s costliest and most inefficient healthcare systems. A policy idea born in conservative think tanks in the early 1990s, the Affordable Care Act put in place market-based solutions to some of the healthcare industry’s most pressing problems.

As with healthcare and climate change, attempts at immigration reform have been scotched by opposition on the right.

Had the act been instituted as planned, it would have had a much broader impact. But red states refused federal money to provide healthcare for their citizens, tanked the healthcare exchanges, and refused to provide legislative fixes for problems within the act.

As a result, though the act was able to provide some much-needed protections, it was not a cure-all for the ailing system - which is why Medicare for All, a government-based healthcare program, has become a core Democratic proposal in the last few years.

For the same reasons, we can expect that Democrats will start to push for more expansive immigration overhauls.

Calls to abolish the Immigration and Customs Enforcement agency may not have made their way into the mainstream of the party, but they have gained traction not only because of a more militant and brutal immigration regime, but because so little has been achieved in immigration reform in the past few decades.

As with healthcare and climate change, attempts at immigration reform have been scotched by opposition on the right. Incrementalist reforms were attempted first in the mid-2000s under George W. Bush and again in the mid-2010s under Barack Obama.

Despite bipartisan efforts to write that legislation, however, anti-immigrant groups killed the reform measures both times. As a result, half-measures like a solution for children brought to the US without documentation and non-enforcement have left undocumented immigrants caught in a broken system with little hope that it will soon be fixed.

The dynamic is rewriting American politics. And it’s why there is little appetite left for centrism and bipartisanship. It’s not that Americans rejected these concepts out of hand; it’s that over the past 15 to 20 years, they have seen few results from centrist policymaking.

They have also witnessed how, in the face of that inaction, these pressing problems have become  significantly worse: medical costs and insurance premiums continue to climb, as do global temperatures and the numbers of undocumented migrants. What perhaps once could have been dealt with gradually now requires massive intervention.

Centrism and moderation are widely praised in the political press, lauded as antidotes to polarisation and partisanship. But they have far less support than they used to. Groups like No Labels, formed to offer a middle way in American politics, failed to find traction, and former Starbucks CEO Howard Schultz’s independent bid for president immediately drew scorn from across the political spectrum.

Perhaps that’s a failing of American politics, and we would all be better off if politicians sought middle ground. But perhaps it’s a rational response to the failures of incrementalism and the impossibility of bipartisanship in the current moment. If so, then the Democratic Party’s lurch to the left isn’t a mistake, but a step in the right direction.