Few clean energy sectors have been threatened as directly by Donald Trump as offshore wind. The president-elect vowed on the campaign trail to end offshore wind development via executive order ​“on day one” of his second term.

Trump has nurtured a hatred for the industry since at least 2006, when he began fighting a wind project off the coast of his golf course in Scotland. He waged a years-long legal battle to block it and ultimately lost before the U.K. Supreme Court in 2015.

But could the Trump administration really stop offshore wind in its tracks?

Experts say Trump won’t be able to deliver on his campaign promise to kill off the industry in a single day, but his administration could stop some development and make things much harder for proposed and planned projects. This, in turn, could stall development of a clean energy resource that is expected to be cheaper than fossil-fueled power once it scales up. That would be good news for power plants that want to protect their market share from cheaper and cleaner competition, but bad news for tens of millions of utility customers and the broader economy.

The Biden administration set a goal of installing 30 gigawatts of offshore wind by 2030, an energy source that is core to several coastal states’ decarbonization plans. This sector in the U.S. is fast-growing — tens of billions of dollars in public and private investment have poured into it in recent years. But it’s still a new industry here, and supply-chain problems and inflation-driven cost escalations have led to project delays and cancellations. Because of those challenges, offshore wind development is already far off-track to meet federal and state goals.

And now comes a newly hostile political environment.

The federal government controls the waters off U.S. coastlines, so it can dictate the siting of offshore wind projects — a notable difference between offshore wind and other types of clean energy. The U.S. Department of Interior puts potential wind development sites out to bid in lease sales.

The Trump administration will have the power to halt those lease sales, and it will be able to slow the processing of key federal permits for projects already in the pipeline.

“There’s a sense that this change will bring a lot of regulatory uncertainty at the federal level,” said Jeremy McDiarmid, managing director and general counsel for Advanced Energy United. ​“All these things create uncertainty in the marketplace, and that makes financing more expensive.”

Shares of European wind-power giants including Danish energy firm Ørsted and wind-turbine manufacturers Vestas and Nordex fell after Trump’s victory, following a broader pattern for clean energy stocks, as markets reacted to fears of a rollback of U.S. clean energy incentives.

Trump’s pledge to end the industry came during a May campaign stop at a New Jersey coastal resort city that’s been fighting offshore wind development over concerns that it’ll harm the fishing industry and spoil views from shorefront properties. During his speech, Trump repeated a claim from offshore wind opponents that the projects kill whales — a theory that federal researchers have debunked.