There’s nothing congressional Republicans can do to stop President Barack Obama’s assertive new moves against carbon pollution. There’s nothing the Democrats can do to help him. And both sides have concluded that trying could make their own political fortunes worse.

Which is why four years ago to the day is going to stand, until at least the end of the decade, as the legislative climax in the climate change debate.

That was the day the House passed sweeping legislation to significantly reduce and limit greenhouse gas emissions, create a new market in carbon release permits and mandate more electricity generation from renewable sources. (Coincidentally, it was also the climactic moment in the career of the bill’s principal sponsor, Edward J. Markey, at least until Tuesday’s special Senate election in Massachusetts.)

In the rearview mirrors of both parties, though, that 219-212 roll call was also the moment that first heralded the indefinite end of the House’s Democratic majority.

Six out of every seven caucus members backed Obama, who had just won the presidency with a commitment to curb climate change as a signature cause. Only eight Republicans joined them. And passage of that bill, four months before health care came up for a vote, did as much as anything to help the nascent tea party movement congeal into a visible force.

When the Democrats lost the House the next year, “yes” votes on cap-and-trade were largely to blame for at least half of the 51 incumbents defeated. Had the Senate debated a similar bill, the odds of a GOP takeover there as well would have gone way up.

That synopsis informs the current politics of environmental policy, where fossil fuels have temporarily replaced Social Security as the touch-and-you’ll-die “third rail” of congressional campaigns.

Today’s Democratic leaders on the Hill know that even sounding all that interested in reviving the global warming debate would turn their party’s projected 2014 losses in the House from slight to significant, complicate their calculus for holding the Senate and put all of their potential 2016 presidential aspirants at a disadvantage.

So they appear entirely content to stay silent while Obama uses his executive powers as assertively as possible to advance his environmental goals. Some proposals the president unveiled Tuesday — doubling the amount of renewable energy generated on federal land, putting thousands of solar panels in public housing projects, creating loan guarantees for carbon-capture technologies, ramping up hydropower production at existing government dams — are going to be difficult to deride as economically misguided or ruinous in any case.

Democrats were thrilled that Obama set an after-the-midterm timetable for finalizing his most controversial proposal: new EPA rules that will limit for the first time heat-trapping pollution from all existing coal-fired power plants, in addition to any new ones.

In other words, the less congressional Democrats have to engage in the greening of Obama’s second term, the better they think they’ll do in November 2014.

Today’s Republican leaders at the Capitol know the other side sees it that way, and they worry that approach could work.

So the GOP’s short-term strategy will be to get out of the way of the president’s proposals — the better to hang his ideas around the necks of Democrats. Their targets are especially those in red states, those most vulnerable to charges they are complicit in an Obama “war on coal” that would kill jobs and drive up the cost of energy.

The party’s eventual nominees for the Senate in Kentucky and West Virginia, along with incumbents Mark Begich of Alaska and Mary L. Landrieu of Louisiana, can expect to hear the accusations particularly often.

This political tactic is the best option for the Republicans because their ability to rebut the president’s policies is nonexistent. Quite simply, they lack the votes to thwart the new climate change agenda.

The GOP could push language through the House preventing the EPA from spending money to write the new rules. But such “limitation amendments” have no chance of acceptance by the Senate, either as part of an appropriations bill or for inclusion in what looks to be an inevitable year-ending catchall continuing resolution.

Speaker John A. Boehner also could win House adoption of one of the special measures allowing Congress to spike a new regulation during its first two months on the books. But that would have slim chances in the Senate, even though only a simple majority is necessary. Even then, an Obama veto would put an end to the discussion.

The strongest weapon the GOP has at the moment is the power to block Gina McCarthy’s promotion from air quality chief to head of the EPA. But keeping that job empty could end up looking obstructionist and punitive. And it would seem justified only if there was clear evidence she didn’t tell the truth at her confirmation hearing this spring, when she said her office wasn’t drafting new carbon-capture requirements for existing power plants.

By late Tuesday afternoon, McCarthy’s path to confirmation before the end of July seemed unchanged by the president’s speech.

The bureaucratic and regulatory pace means Obama will be a lame duck by the time all these proposals are put in place, if legal challenges don’t slow the process further.

While the Supreme Court has affirmed the EPA’s power to regulate greenhouse gases under the Clean Air Act, the legal parameters of such an effort are open to wide interpretation, and aggrieved power companies are destined to go to court to test those limits.

So it’s not unreasonable to expect that, four years from now, the justices will be announcing a ruling that serves as the next climactic moment in the climate change debate.