President Obama has announced or will soon propose important protections for clean water, clean air, threatened species and threatened landscapes. Mitch McConnell, the Senate majority leader, and other Republicans in Congress are trying hard not to let that happen — counterattacking with a legislative blitz not seen since Newt Gingrich and his “Contract With America” Republicans swept into office after the 1994 midterm elections bent on crippling many of the environmental statutes enacted under Presidents Johnson and Nixon. Bill Clinton threatened or used vetoes to block that assault. Mr. Obama should be prepared to do the same.

The usual complaints about “executive overreach” and “job-killing regulations” have been raised. But beneath all the political sound bites lies a deep-seated if unspoken grievance that Mr. Obama is actually trying to realize the promise of laws that Congress passed years ago but wouldn’t stand a chance with today’s Congress. The nonsense about regulatory overkill has also infected the presidential campaign, the latest manifestation being a batty suggestion from Gov. Scott Walker of Wisconsin to shift the functions of the Environmental Protection Agency to the states. Mr. Walker presumably hopes to please business, but it would be hard to think of anything more unsettling to executives than the prospect of having to operate in 50 states with 50 different sets of rules — or anything more harmful to the evenhanded enforcement of federal environmental laws.

Here are some of the points of Republican attack:

Clean Water In May, the administration approved a long-overdue rule greatly increasing the number of streams and wetlands protected by the Clean Water Act. The rule will ensure cleaner drinking water and do little to impede responsible development. Even so, the House has already passed a stand-alone bill to cripple it; in the Senate, John Barrasso of Wyoming, who says the rule would “devastate” private property rights, introduced a similar bill in April. Mr. Obama should veto any such measure.

Climate Change Mr. Obama has made skillful and timely use of his authority under the Clean Air Act to increase automobile efficiency, crack down on mercury emissions and reduce harmful smog, but his most important initiative lies ahead: a final rule due later this summer to reduce carbon dioxide emissions from existing coal-fired power plants. The rule, which requires individual states to develop emission-reduction plans tailored to their energy mix, is central to the president’s pledge to reduce America’s greenhouse gas emissions by 28 percent from 2005 levels by 2025, and to his credibility as a leader in the fight against global warming. Mr. McConnell, in servitude to the coal industry, has been urging states not to cooperate, while sending unhelpful messages to the rest of the world that Mr. Obama will not be able to deliver. The Republicans are weighing how to undercut the rule, but there’s hardly any doubt they will try.