(Photo by Chip Somodevilla/Getty Images)

French President Emmanuel Macron, speaking in front of Congress, said that one day, the US will come back to the Paris agreement, which Trump pulled out of last year.

So what's in the deal?

The Paris agreement came together in 2015. Representatives from close to 200 countries gathered in the French capital and pledged to take decisive action on climate change.

Under the accord, countries that signed on agreed reduce their carbon output and halt global warming below two degrees Celsius by the end of the century.

The deal was heralded as "the end of the era of fossil fuels" and "a victory for all of the planet" over the days that followed.

Why Trump backed out

When he announced the US would leave the agreement, Trump cast it as a humiliating defeat for American workers that unfairly advantaged foreign countries.

"At what point does America get demeaned? At what point do they start laughing at us as a country?" Trump asked in June.

Trump, who has governed with an "American First" policy, said that in backing out of the agreement, he was carrying out the will of the people who voted for him.

"I was elected by the citizens of Pittsburgh," Trump said, "not Paris."

Currently, the United States and Syria are the only countries in the world not in the agreement. (Although Syria said last year that it would join onto the accord.)