A mammoth effort by leaders around the world over the last few years has culminated in the recent deal in Paris where countries promised to dial back carbon emissions in a bid to save the planet from global warming. But could President Donald Trump totally undo that effort in his presidency, if he is elected, thus scuttling an important agreement and further setting Earth on a destructive course with regards to climate change? That’s the dark cloud that is currently hanging over the architects of the Paris Agreement, set to start in 2020 but now appears likely to start much earlier.

With 99 countries and the European Union on board, work could begin soon on putting the Paris Agreement into practice. And with Trump within striking distance of the presidency, and considering his past comments about global warming and climate change being a hoax invented by the Chinese, there are significant question marks hanging over the deal. Trump has said in no uncertain teams he would pull the United States out of the climate agreement if elected, which would certainly kill the deal’s teeth.

That’s why many leaders are rushing to ratify the agreement so that it is in force before the U.S. vote, which would keep a country from withdrawing over the next five years. That could happen as soon as the Nov. 7-18 UN climate talks, and there are still many hurdles that will need to be overcome.

According to a statement from the European Comission, governments agreed under the Paris accord to “a long-term goal of keeping the increase in global average temperature to well below 2°C above pre-industrial levels; to aim to limit the increase to 1.5°C, since this would significantly reduce risks and the impacts of climate change; on the need for global emissions to peak as soon as possible, recognising that this will take longer for developing countries; to undertake rapid reductions thereafter in accordance with the best available science.”