The Paris Agreement is not that restraining. It mostly involve making known that your country is part of the agreement and regularly stating your objectives, efforts and contributions. It's not forcing results or even efforts, it's a symbolic agreement :
In the Paris Agreement, each country determines, plans and regularly reports its own contribution it should make in order to mitigate global warming. There is no mechanism to force a country to set a specific target by a specific date, but each target should go beyond previously set targets.
Moreover, Donald Trump may have said that he was making the USA to leave the Paris Agreement, but he actually announced the intention to do it, which means that canceling that announcement by not withdrawing would be enough, no need to re-join according to my interpretation :
In 2017, U.S. President Donald Trump announced his intention to withdraw the United States from the agreement, causing widespread condemnation in the European Union and many sectors in the United States. Under the agreement, the earliest effective date of withdrawal for the U.S. is November 2020.