President Trump stepped up his attack on federal environmental protections Tuesday, issuing an order directing his administration to begin the long process of rolling back sweeping clean water rules that were enacted by his predecessor.

The order directing the Environmental Protection Agency to set about dismantling the Waters of the United States rule takes aim at one of President Obama’s signature environmental legacies, a far-reaching anti-pollution effort that expanded the authority of regulators over the nation’s waterways and wetlands.

The contentious rule had been fought for years by farmers, ranchers, real estate developers and others, who complained it invited heavy-handed bureaucrats to burden their businesses with onerous restrictions and fines for minor violations.

Obama’s EPA argued that such claims were exaggerated and misrepresented the realities of the enforcement process of a rule that promised to create substantially cleaner waterways, and with them healthier habitats for threatened species of wildlife.

The directive to undo the clean water initiative is expected to be closely followed by another aimed at unraveling the Obama administration’s ambitious plan to fight climate change by curbing power plant emissions.

“It is such a horrible, horrible rule,” Trump said as he signed the directive Tuesday aimed at the water rules. “It has such a nice name, but everything about it is bad.” He declared the rule, championed by environmental groups to give the EPA broad authority over nearly two-thirds of the waterways in the nation, “one of the worst examples of federal regulation” and “a massive power grab.”

While the executive orders are a clear sign of the new administration’s distaste for some of the highest profile federal environmental rules, they also reflect the challenge it faces in erasing them. Both the climate and the clean water rules were enacted only after a long and tedious process of public hearings, scientific analysis and bureaucratic review. That entire process must be revisited before they can be weakened. It could take years.