On the heels of contentious climate talks in Azerbaijan, negotiators from around the globe are descending on Busan, South Korea, this week with another formidable goal: to hammer out the world’s first treaty designed to tackle plastic pollution’s explosive growth.

On the table is a proposal that aims to cut down on the millions of tons of plastic waste discarded each year. And a broad coalition of nations is seeking to go a step further and rein in plastic production, with a focus on restricting single-use plastic.

That notion had gained traction leading up to the final round of talks in Busan, with even the United States, a major plastics producer, tentatively backing the United Nations-led effort.

Then came the election of Donald J. Trump.

Now, few expect the United States to sign on to an eventual treaty at all. And with deep-seated opposition from oil and gas nations like Saudi Arabia and Russia — which, like the United States, produce the fossil fuels used to make plastic — some delegates are wondering whether any agreement is possible by the scheduled end of the talks on Sunday.

“The U.S. really engaged on this, but if they step back, it’s a big disappointment,” said Ndiaye Cheikh Sella, a delegate for Senegal and the chief of staff of the country’s environmental ministry.

There is one consensus among most delegates: The world has a colossal plastic waste problem.

The world produces nearly half a billion tons of plastic each year, more than double the amount from two decades ago, and much of that turns up on coastlines and river banks, as well as in whales, birds and other animals that ingest them. Researchers have estimated that one garbage truck’s worth of plastic enters the ocean every minute.