The election of Donald Trump has left the Democratic party defanged. Despite winning the popular vote, the Democrats now face four years of a radically right wing executive and at least two years in the minority in both houses of Congress.

But as they cast around for succor, there is still one major institution they overwhelmingly control: cities. Of the 20 biggest US cities, only Fort Worth (Texas), San Diego (California), and Jacksonville (Florida) have Republican mayors. Across the whole US, the more densely inhabited the area was in the 2016 presidential election, the more likely it was to vote Democrat.

What’s more, cities are “the one institution today that still works, where government functions, where trust levels are double the levels of other institutions,” says Benjamin Barber of Fordham University, an acclaimed social scientist and author of If Mayors Ruled the World: Dysfunctional Nations, Rising Cities.

Barber, a fast-talking native New Yorker and former outside advisor to president Bill Clinton, argues that inter-urban collaboration can improve security, ease the refugee crises, and enable cities to combine to buy technology like trash-to-green-energy incinerators that would otherwise be prohibitively expensive. Earlier this year, he talked to Quartz about the Global Parliament of Mayors, his project that aims to function like a United Nations for cities.

After Trump’s election, the mayors of a number of major cities have already said they will do their utmost to protect undocumented immigrants in their metro areas. We went back to Barber to find out what else is in their power to ensure good, progressive governance for their populations. The interview has been lightly edited for length and clarity.

Quartz: Very broadly, what role could mayors play over the next four years; both in terms of effective governance, and in standing up for citizens who may be alienated or discriminated against by the next administration?

Barber: Cities are going to become the most important, constructive alternative to a Trump agenda.

Over the last 10 years we have already seen a powerful emergence of cities as primary spaces for progressive and majority action, for the protection of diversity, for dealing with immigration to the US, higher minimum wage, gender relations and so on.

This is not something new. We were already witnessing the devolution of authority and power and moral authority as the result, even before Trump, of the breakdown of national governments. Whether it’s Brexit, or right-wing governments in Poland and Hungary, or anti-immigrant feeling in France and Belgium and Holland, or a crazy man in the Philippines violating civil rights, or Brazil with no national government at all. The election of Donald Trump is obviously a further sign of this kind of dysfunction. He is somebody who is in fact an enemy of national governments, an enemy of the intervention by the state on behalf of justice, redistribution, etc.

In the US, our check against the abuse of power has been the separation of powers. The problem is when one party occupies all three branches of government as they do…the horizontal separation of powers is no longer an adequate check. But there is also a vertical separation of powers, called federalism.

I believe the vertical separation of powers is going to play an important role because in fact the blue parts of the American map are urban. It’s not East and West coast…it’s urban versus suburban and rural. Take climate change, for example—an area where cities have a very large role to play. About 80% of greenhouse gas emissions come from cities and cities also control about 80% of GDP. They can do a lot to combat climate change, whether or not Trump undermines the COP21 agreement.

In what other areas do cities have the power to provide where the federal government might fail?

On the economic side, one of the most important things the Democrats have been fighting for in Washington, unsuccessfully, was a national minimum wage. A lot of cities are now imposing a minimum wage, which they have a right to do. States can do it too. So, despite the refusal of the Trump administration to develop a national minimum wage standard, cities can get a minimum wage for 60-70% of the American population, and a lot of states may follow.

Or, let’s just say the Supreme Court becomes occupied by Trump appointees and it kills Roe v. Wade and in effect says abortion is not a right. Under current constitutional order, states and localities can themselves control that. Roe v. Wade guarantees a national right but even in the absence of a national right, if it is overturned, cities and states can themselves insist on those rights. In New York and Chicago, and Atlanta and New Orleans and San Diego, they can say “abortion is legal and protected.”

In practice, how could “sanctuary cities” defy a Trump immigrant deportation scheme?

The deportation force comes into New York and says “we’re deporting these people,” and the New York Police Department and the state police refuse to cooperate, and refuse to arrest people to protect them. That’s a fairly radical thing, because there you have a confrontation between national and local law. But you don’t want to forget these fundamental facts: the majority of Americans live in cities, the majority of Americans voted against Trump, and the majority of wealth is generated in cities.

This is a majority in the places where it lives and works insisting on its rights! Insisting that on the one hand it will do things the federal government fails to do, and on the other hand that it may refuse to do things that it regards as unconstitutional that the federal government tries to do. The second is more radical and dangerous and difficult, but it’s possible. The first is completely possible and legal, and there’s nothing Trump can do about that at all. Trump can’t say, “I’m against a national minimum wage law and therefore I’m going to stop Los Angeles from having one.”

Can can we expect mayors to actually confront the Trump administration?

They can and will—some already are. And more importantly they need to do it together. It will therefore be through the US Conference of Mayors, through our new Global Parliament of Mayors, through organizations like the C40 Cities that work on climate change. One by one, they’re not very strong. But when cities act together and pool their resources, their populations, their majorities, they become very strong indeed.

A number of cities have already banned fracking, for example. You might say, “Well, fracking doesn’t happen mainly in cities.” Well, some does and it’s a symbolic thing. But now imagine that 6,000 American mayors all together say, “There will be no fracking in our cities.” That could make a Trump administration’s national strategy to do massive fracking much, much more difficult.

Who would you expect to be the likely leaders of a movement like that?

I would expect the larger and more influential the city, the larger the population and its resources, and therefore, the more likely it would be affected by new federal policies that are inimical to, say, equal marriage, to minimum wage, to immigration. I think they will speak out.

Already, Mayor Bill de Blasio in New York has a program that gives unregistered, undocumented immigrants the right to apply for a New York ID card and use it, even though technically they’re illegal. In Los Angeles, Eric Garcetti is another visionary, powerful mayor, Mayor Kasim Reed in Atlanta, Mayor Marty Walsh of Boston. I think you will find that, not because they’re brave—although I think they probably are—but because it will be in the interest of the democratically elected leaders of what in fact is a majority of Americans who voted against Trump. This is a place where you can have legitimate, democratic dissent, but more importantly, legitimate, democratic action on behalf of progressives—whether or the federal government wants it.

What can mayors do on things like repealing Dodd-Frank?

Trump said he is going to bring back the manufacturing jobs and that he is going to prevent the export of the manufacturing and automobile economy. He’s a total fool and liar on that score because he has no power to do so.

He cannot compete with wages; the only way he’s bringing back those jobs he promised to Detroit and Cleveland is at $0.50 an hour. Obviously Americans aren’t going to work for $0.50 an hour. That’s what you have to do to compete, to bring the jobs back. The reasons the corporations leave is because they can get cheap labor, lower safety standards, and a better profit on their returns elsewhere. As long as they get that, it doesn’t make a damned bit of difference. So, you’re right to say that cities are not in the position to confront the difficulty of an unregulated, global profit-mongering economy—but nor is the US government! Nor is Trump!

But this is a slightly different question to bank regulation, right?

I know; he probably will dismantle Dodd-Frank.

Can cities do everything in every area? Obviously not. But in many of the areas where Trump may take America in a regressive direction, cities will be a powerful antidote, a powerful riposte, a powerful counterpoint, which will preserve the rights and dignity and jobs and a lot of other things for the majority of Americans.

The old parties—the Republicans and Democrats—they’re absurd, they don’t work, they still argue 19th century issues of capitalism and socialism in a world of an informational global economy. It doesn’t make sense. I think you may see the emergence of a kind of urban party, a party of the kind of people who live in cities all over the world, who say “never mind socialism and capitalism.” The real distinction is between people who live in cities and prize diversity and open society and bridges and intercourse with other nations and cultures and creativity and entrepreneurship and innovation, against a backward-looking, non-urban population that are the opposite.

What could be the response, either individually or through collaboration, to something like the repeal of Obamacare?

New York city has, for example, a guarantee of housing for homeless people. That’s a sort of social safety net. The problem for cities doing those things is they don’t necessarily have the resources. But here’s the fact—cities generate 80% of GDP and and tax revenue. Cities may have to start saying, “I’m sorry, we’re not turning all this money over, we’re not gonna give them to you and then you basically give them to the rich. We’re gonna retain them, and give them to the poor and the homeless and those you refuse to help.”

So, then you get into a battle about resources, about taxation and revenue. That’s a fairly radical battle but, again, I think radicalism isn’t something cities are forcing on the nation; radicalism is something that Trump and his people are imposing on cities. It’s one thing for Washington to say it’s not going to do healthcare and social safety nets; it’s another to say we will not let cities do it.

Is it likely that cities will actually be able to retain more of their tax revenue? How do you think Trump would react to a battle like this?

It’s two days after the election, I’m not going to predict the future 10 years down the road. I am stating facts. The fact is, cities generate 80% of GDP and the greater proportion of tax revenues. The fact is, they give a lot of it away to the national government and don’t get it back. The fact is, they do that and have done it willingly because the national government has taken care of a lot of things that cities don’t have to take care of—like social security, like social safety nets, like redistribution. If we now have a government that refuses to do any of those things, I think that becomes a powerful motivation for that struggle.

I suspect that when Trump actually gets to Washington, sits in the White House, and realizes the responsibility of national power, a lot of the shit that he talks is just going to go away. But if I’m wrong and he implements a program around the kinds of things he’s said, I think you will see serious resistance—both protests in the streets and also civic resistance on the basis of federalism and the rights of cities.

If national governments refuse to uphold the rights of life, liberty, and property that are the basis of the social contract, then they default on the social contract. Sovereignty passes back to those who make good on the social contract. If the federal government says it doesn’t believe in climate change and will allow sustainability to disappear and allow climate change to ruin the world, then cities will say, “You have forfeited your responsibility for our lives…it is our responsibility to protect that, and we will do that and we will take the resources that we need.”

You could, in fact, frame this in a way that plays into Trump’s agenda of “draining the swamp” of Washington, right? He could do that by devolving more power to cities.

That’s a very important point. Because there is an ironic contradiction in his whole program: it’s the Republicans, traditionally, who have wanted to see a devolution of power, who wanted to empower states and localities.