Agenda 21 isn’t getting the attention it once did. Five years ago, the much-criticized United Nations environmental manifesto was all over TV news and conservative talk shows, denounced by Glenn Beck and others as a sinister globalist threat to American sovereignty and liberty.

That debate has more or less quieted down. But the opponents of Agenda 21 haven’t gone away; they have merely spread out, into the politics of cities and counties planning for the future. They aren’t winning everywhere, but they have acquired access to funding and a collection of allies that makes it wise to pay attention to them.

In many cases, they are avoiding some of their most incendiary rhetoric of a few years ago -- they are “shape-shifting,” in the words of Karen Trapenberg Frick, a scholar at the University of California, Berkeley, who has studied the movement. The campaign has become subtler in its approach. But it is making its presence felt almost everywhere public arguments are taking place over urban design and public transportation.

If you are at all familiar with the Agenda 21 controversy, you probably will find this a little strange. The document, approved at a U.N. conference in Brazil in 1992, is devoted almost entirely to global poverty, pollution and the need to conserve natural resources. It scarcely says anything about transportation or urban design.

Reading through Agenda 21’s turgid pages, it’s hard to find much that would frighten most people. I came across only two passages that looked like possible candidates for serious urban controversy. One was a recommendation that governments develop “efficient, cost-effective, less polluting and safer rural and urban mass transit.” The other talks about “reducing the need for motor vehicles by favoring high-occupancy public transport.” This is the sort of innocent language that mayors in American cities use every day. And in any case, Agenda 21 is purely voluntary. Governments are free to ignore it, and for the most part, they have been doing so for more than two decades.

But to a sizable number of conservative activists, this seemingly innocuous text is merely coding for a scheme to change the very form of urban existence by imposing “smart growth” master plans, “visioning” and a whole range of freedom-destroying collectivist experiments. Beck’s 2012 novel, itself titled Agenda 21, paints a picture of future dystopian cities whose residents are stripped of their individuality by being confined to “ubiquitous concrete living spaces.” Last year, a writer for the Washington, D.C.-based Selous Foundation warned that the “stated goal” of Agenda 21 is “to change people’s behavior through restrictions in land use, herding people into dense inner-city housing, and restricting mobility to force Americans out of their cars and into government-controlled mass transit systems.” A couple of years ago, an online newsletter called Ecologic told its readers flatly that “smart growth is Agenda 21.”

Conspiracy theories have existed in the United States since the country was founded, and most of them have faded away without doing a great deal of damage. The “AgEnders,” as the Agenda 21 opponents often call themselves, are likely to meet the same fate eventually. But there are a couple of reasons why they have managed to stick around as long as they have.

The most important reason has to do with the relationships formed between AgEnders and other well-financed transit opponents at the national level. The most important anti-21 activist is Tom DeWeese of Warrenton, Va., whose organization, the American Policy Center, has been fighting Agenda 21 almost since its passage in 1992. DeWeese wrote recently that the international policies of the document “go directly into local communities, disguised as innocent-sounding development projects or historic preservation -- drastically changing our way of life.”

Disciples of DeWeese have been involved in several anti-transit campaigns in the past few years, thanks in large part to their alliance with Americans for Prosperity, the conservative group founded by the oil-billionaire Koch brothers. Americans for Prosperity has formed branches in many of the cities that have voted on major transit projects, and it can bring in a virtual repertory company of speakers to inveigh against these projects.

This coalition was active in Georgia in 2012, when voters in metropolitan Atlanta turned down a sales tax increase for transportation that had the support of virtually all local elected officials and business leaders. It was at center stage the same year in Alabama, where the legislature passed a resolution prohibiting any government involvement with or participation in Agenda 21. It achieved mixed results in 2014 in Indiana, failing to block a bill in the legislature that allowed a transit referendum in Indianapolis but amending the bill in a way that prevented the city from spending money on a light rail system.

But the biggest victory for the anti-transit forces was the one that took place early last year in Nashville. Mayor Karl Dean and his administration were promoting a new streetcar that would run between gentrifying East Nashville and wealthy West End. The city’s business community was firmly behind the project, as was the influential leadership of Vanderbilt University. The federal government was poised to kick in $75 million. Final approval seemed to be just a formality.

Then Americans for Prosperity, recognizing that it couldn’t stop the streetcar at the city level, began working the state capitol. Tennessee’s Republican-controlled legislature had already passed a resolution denouncing Agenda 21 as “a comprehensive plan of extreme environmentalism, social engineering and global political control.” Persuading the same lawmakers that the Nashville streetcar was part of the global urbanist cabal didn’t prove very difficult. Both the Senate and House passed bills giving the legislature control over adoption of the system. That effectively made the Nashville project impossible to execute. The city had to tell the Obama administration that it wouldn’t be taking the money.

It would be a stretch to claim that the AgEnders and Americans for Prosperity were the only problem the streetcar project had. There was considerable local sentiment against it on the grounds that, for all the expense, it wouldn’t do anything to relieve downtown traffic congestion. Even the project’s backers acknowledged that the Dean administration hadn’t done a very effective job of mobilizing support for it. Nevertheless, the killing of the Nashville streetcar -- using a strategy of persuading the state to nullify a local decision -- was a crucial moment in the continuing ideological war over mass transit in American cities.

Since then, anti-transit forces have thrown their support behind a variety of local efforts. They are fighting against a bus rapid transit system in downtown Albuquerque, a project for which backers have sought $80 million in federal funds. They also have generated sufficient opposition to a proposed streetcar system in Milwaukee to make it a decisive issue in that city’s upcoming mayoral campaign.

Not all of these ventures have focused on Agenda 21; some of them have stuck to local arguments and opposed transit funding strictly on fiscal and libertarian grounds. But it seems fair to say that wherever a significant transit or urban planning challenge is launched, the theories of the AgEnders are never entirely absent from the discussion.

That was the case this November in Utah, where the anti-transit movement won another notable victory: Proposition 1, a sales tax increase aimed at paying for transportation improvements in 17 counties surrounding metropolitan Salt Lake City, narrowly failed in the most important jurisdiction, Salt Lake County, where the city is located. This was a case where proponents of the tax, including virtually the entire metro-area business leadership, vastly outspent the opponents, who were directed in a low-budget campaign by the Utah branch of Americans for Prosperity. The opposition hammered away at the argument that 40 percent of the revenue generated by the tax increase would go to transit rather than roads, and this ultimately proved decisive.

Agenda 21 didn’t figure in the public discussion in Utah, but the Tea Party saw Agenda 21 as relevant to the entire debate over the area’s future. A visit to the website No Agenda 21 yielded denunciations of the U.N. initiative and criticism of Proposition 1 in almost equal measure. One of the Tea Party targets was Envision Utah, the long-range planning body that has won national recognition for its consensus-based approach to difficult issues. Some of the Tea Partiers appear to have zeroed in on Envision Utah as a target for their resentments.

But the vote on Utah’s Proposition 1 wasn’t the only major transportation decision on Election Day. While Salt Lake City voters were showing their transit skepticism, those in Seattle were making an opposite choice: endorsing their own Proposition 1, a $930 million spending package designed to improve the city’s transit system and devote more resources to street maintenance and pedestrian and cyclist safety. Neither Americans for Prosperity nor the AgEnders were very visible in Seattle; they may have considered it a lost cause. The transportation package, backed by Mayor Ed Murray and a diverse array of major corporations, passed with more than 59 percent of the vote.

The lesson from all these recent skirmishes seems to be that the anti-transit coalition can be a potent force in a community where a significant cadre of opposition already exists, based on specific local grievances. Then Americans for Prosperity can come in and stir up the critics, Tea Party activists can work the grassroots and the AgEnders can rally their troops with frightening visions of urbanist apocalypse. Where those pre-conditions don’t exist, there aren’t going to be many startling defeats for mass transit and urban planning.

But there are going to be some surprises: The next one will most likely be in a place where you didn’t see it coming.