But we are far past the point when we should be discussing whether climate change is a live risk. The Pentagon calls it a “threat multiplier” in vulnerable regions of the world. The National Intelligence Council says climate change “will almost certainly have significant effects, both direct and indirect, across social, economic, political, and security realms during the next 20 years.” Firms like BlackRock, Goldman Sachs, Citigroup, and Shell, among others, have produced serious climate reports focused on the transition needed to meet the goals of Paris. And just look at the signals from nature, at the dozens of “100-year” events—floods, superstorms, droughts, wildfires, record heat waves—taking place in the United States and around the world in recent years. Weather-related losses have tripled since the 1980s.

In short, whether to stay in the Paris regime is not a close call. It is not hard. There is no significant outside constituency arguing for America to leave. There is a massive outside constituency—world leaders, Fortune 100 CEOS, civil society—urging us to stay, even if the price for Trump staying is a downward adjustment of our target. The Trump team now appears to be getting it wrong. Where are the determined internal voices for getting this right? Where is the vaunted national security team to protect our standing, our reputation, our honor? Where are the grownups to channel the near-consensus of American business and prevent this train-wreck of a decision?

But we have to confront the likelihood that this happening. So, what do we do then?

What we don’t do is wring our hands or lose hope. All over the United States and all over the world we must resolve to defeat the Trump administration in its effort to toss climate change overboard.

Around the world, I believe countries will stay in the Paris climate agreement and work to build it into a regime that will enable us to meet the climate challenge. They need to elaborate follow-on guidelines, rules and procedures in a manner faithful to the essential balance of the accord. And, with others, I will encourage them to do this in a manner that will pave the way for re-entry by an enlightened American administration in the years ahead.

In the United States, the already strong efforts of our states and cities will loom even larger, demonstrating to ourselves and the world our commitment to confront climate change. States from California, Washington, and Oregon to Minnesota, Illinois, New York, New England, and many others are dedicated to strong climate action and will examine whether there is still more that they can do. Many more states, both red and blue, are charging ahead in developing wind and solar energy.

The dozen U.S. cities that are part of the global C-40 group on climate change account for 25 percent of U.S. population and 30 percent of U.S. GDP. In Mexico City last December, led by Mike Bloomberg, they promised to deliver action, regardless of what the new Trump administration decided to do. These and dozens of other committed U.S. cities have a more important role to play than ever.