The number wasn’t a big reveal – the Obama administration signaled last November, in a joint announcement with China, that it wanted to commit the U.S. to greenhouse-gas emissions cuts of 26-28 percent below 2005 levels by 2025.

Still, advocates for bold U.S. action, like Alden Meyer, director of strategy and policy for the Union of Concerned Scientists, were happy to see the State Department formally submit that target to the U.N. on Tuesday, hopeful the move will help build momentum toward a strong agreement when the world gathers to talk climate in Paris late this year.

“The U.S. proposal demonstrates real leadership, and should encourage other countries to put forward solid offers in the run-up to Paris,” Meyer said in a statement.

It encouraged Mitch McConnell to put out a rather remarkable press release, one with an undercutting intention a lot like that senatorial letter to Iran regarding a nuclear deal a few weeks ago.

“Considering that two-thirds of the U.S. federal government hasn’t even signed off on the Clean Power Plan and 13 states have already pledged to fight it, our international partners should proceed with caution before entering into a binding, unattainable deal,” the Senate’s majority leader said.

He doesn’t have very many Republicans with him, but the president is striding forthrightly down the path of addressing climate change, and really has been since June 2013, when he announced his Climate Action Plan. That still serves, more or less, as the “how we’ll do it” for the U.S. in reaching its emissions target.

The Clean Power Plan that McConnell so reviles flowed from it, along with various regulatory actions now in the works, such as fuel-efficiency standards and standards for heavy-duty engines and vehicles. In mid-March, as well, Obama signed an executive order intended to cut the federal government’s greenhouse-gas emissions by 40 percent from 2008 levels by 2025, and boost the share of electricity the government gets from renewable sources to 30 percent in the same time frame.

It’s all been enough to earn the president favorable reviews from the climate crowd, which seems to recognize there is only so much the chief executive can do solo. As Meyer, from the Union of Concerned Scientists, put it on Tuesday, “While the United States can and should do even more to reduce its emissions over the next decade, the U.S. offer is quite ambitious, given Congress’ unwillingness to take any action to deal with climate change.”

Ahead of the Paris UN negotiations, countries have until October to submit their emissions targets; the hope is that in aggregate they’ll be sufficient to limit the increase in global temperature to 2 degrees C (3.6 F) “above pre-industrial levels.” Or at least close enough to make the Paris talks viable.

March 31 had been held out as an informal deadline for submissions, officially referred to as Intended Nationally Determined Contributions (INDCs). Most countries let it slide, but with the EU, the U.S. and a few others on board (and counting China’s November pledge), the White House tried to make a case for momentum, noting in a fact sheet that “countries representing over 50% of global CO2 emissions have either announced or formally reported their targets.”

Read more about the importance of INDCs on Breaking Energy here.

However, the tough nuts might well be the poorer nations with faster-growing economies, who feel they haven’t put the world in the mess it faces, so why should they pay the price for fixing it?

In that joint announcement with the U.S. last November, China said it would stop growing its emissions by 2030, and Mexico last week said it would do the same by 2026. The hope is that these commitments will invite strong moves by big countries like India and Brazil. As Brian Palmer put it in an article for onEarth, the Natural Resources Defense Council’s magazine, “Mexico’s participation may help persuade other developing countries that the process can work for them.”