The pro-business American Legislative Exchange Council, known as ALEC, has pushed for many of the pre-emption laws. More recently, however, it has adopted the methods of its opponents. It has helped policy makers in local government make laws to reduce the size of government, for instance, even when states decline to do so.

One division of ALEC, called the American City County Exchange, has most notably pushed for local right-to-work laws to allow workers who are members of a union to opt out of paying dues. Yet in other cases, it has drafted legislation to prevent cities from coming up with their own laws, including on issues like plastic bag bans and containers for composting.

“Sometimes cities and counties overstep the powers they’ve been given,” said Jon Russell, director of the exchange and a town councilman in Culpeper, Va. “There are certain times states and cities are going to disagree, but for the most part, we’re going to figure out ways to resolve certain regulatory issues while staying in our lanes.”

The demographics of big urban centers — often more liberal and diverse than other parts of the country, and more likely to be governed by a single party — foster more progressive policy-making than elsewhere.

And that policy-making does seem to bubble upward to the national level. Workers’ rights are one of the main focuses of today’s urban politics, and several such city policies are now getting state and national attention, including in the presidential campaign. Paid sick leave is an example. The first city to require it was San Francisco in 2006. It is now the law in 23 cities and states, and President Obama last fall required federal contractors to provide it. (Meanwhile, more than a dozen states have pre-emption laws to stop cities from requiring paid sick leave.)

Minimum wage is another example. SeaTac, Wash., passed a $15 minimum wage in 2013. Nearby Seattle followed, and then so did San Francisco, Los Angeles, Mountain View, Calif., and Emeryville, Calif.

Fourteen states have since changed their minimum wage laws, two bills in Congress would do the same nationally, and all three Democratic presidential contenders have said they would raise the federal minimum wage.