As president, Donald Trump’s sweeping attempts to roll back federal environmental regulations were often stymied — by the courts, by a lack of experience, even by internal resistance from government employees.

But if he retakes the White House in November, Mr. Trump would be in a far better position to dismantle environmental and climate rules, aided by more sympathetic judges and conservative allies who are already mapping out ways to bend federal agencies to the president’s will.

“It’s going to be easier,” said Myron Ebell, who led the transition at the Environmental Protection Agency after Mr. Trump won in 2016. “They’re going to have better people, more committed people, more experienced people. They will be able to move more quickly, and more successfully, in my view.”

On the campaign trail, Mr. Trump has promised to repeal federal regulations designed to cut greenhouse gas pollution that is rapidly heating the planet. Many of his allies want to go further. They are drafting plans to slash budgets, oust career staffers, embed loyalists in key offices and scale back the government’s powers to tackle climate change, regulate industries and restrict hazardous chemicals.

Those plans, while wildly ambitious, may be more attainable next time around. Perhaps the biggest change in Mr. Trump’s favor is that over the past two years, the Supreme Court’s conservative supermajority has significantly curbed the legal authority of the government to impose environmental rules on businesses.