I decided to ask Chat and his answer is pretty good.

The authority of a President to directly end electric vehicle (EV) mandates in states is limited. EV mandates are typically implemented through state-level regulations or legislation, and the power to enact or rescind such mandates primarily lies with state governments rather than the federal government.

However, a President could indirectly influence the situation through various means:

Executive Orders: While a President cannot directly overturn state laws or regulations, they can issue executive orders that may impact federal policies related to EVs, such as fuel efficiency standards or federal incentives for EV adoption.

Federal Funding: The President could influence federal funding allocations, grants, or incentives related to EVs, which might indirectly affect the implementation or continuation of state-level mandates.

Advocacy and Persuasion: Presidents often use their platform to advocate for certain policies or priorities. A President could publicly express opposition to state-level EV mandates and attempt to persuade state governments to reconsider or repeal them.

Legal Challenges: In some cases, the federal government may challenge state laws or regulations in court if they believe they conflict with federal law or constitutional principles. However, this approach would likely face significant legal hurdles and may not be successful.

Ultimately, while a President can exert influence on the broader conversation surrounding EV mandates, the ability to directly end such mandates in states is limited by the principles of federalism, which grant significant autonomy to state governments in matters of regulation and legislation.