The United States can’t withdraw until November 2020 from the Paris Climate Agreement. A country must wait three years to announce its withdrawal. Even then, a year must pass from the notification date to the withdrawal.
Now Trump could play hardball and just pull out, but he risks sanctions against the USA, which would hurt the economy that he talks so highly of and alienate our allies.
Even though Trump made his proclamation the United States is still part of the agreement between now and November 2020. If Trump loses a re-election (For sure!), his successor could promptly rejoin in January 2021.