When President Joe Biden convenes a virtual climate summit on Thursday, he will bring together 40 world leaders and unveil a target for the United States to reduce greenhouse gas emissions that he hopes will serve as an example to the world.

But just as he must calibrate the impact of emissions on global warming, in making his calculations, he must also find a way of balancing the demands within his own party between climate change activists and blue-collar voters who worry about their jobs while Republicans in Trump country see an opening for attack.