WASHINGTON/BRUSSELS (Reuters) - The United States formally exited the Paris Agreement on Wednesday, fulfilling an old promise by President Donald Trump to withdraw the world’s second-largest greenhouse gas emitter from the global pact to fight climate change.But the outcome of the tight U.S. election contest will determine for how long. Trump’s Democratic rival, Joe Biden, has promised to rejoin the agreement if elected. “The U.S. withdrawal will leave a gap in our regime, and the global efforts to achieve the goals and ambitions of the Paris Agreement,” Patricia Espinosa, executive secretary of the U.N. Framework Convention on Climate Change (UNFCCC), told Reuters. The United States still remains a party to the UNFCCC and Espinosa said the body will be “ready to assist the U.S. in any effort in order to rejoin the Paris Agreement”. Trump first announced his intention to withdraw the United States from the pact in June 2017, arguing it would undermine the U.S. economy. The administration formally served notice to the United Nations one year ago on Nov. 4, 2019.