Excerpts from Books and Wikipedia
"In June 2017, however, President Donald Trump announced that the United States intended to withdraw from the agreement. Under the terms of the agreement [2015 Paris COP], the earliest effective date of withdrawal for the United States would be November 2020. As of November 2017, the agreement has been ratified by 170 members. The only two major emitters who have not ratified are the United States and Russia, representing about a quarter of global emissions. Russia has indicated it does not intend to ratify before 2019 at the earliest." [Romm, p. 155]