It might be doable via executive order.
For instance, could he cut off law enforcement funding if states did not agree? I think that would bring most states to their knees in short order.
Of course, the downside is that it could be reversed by the next President. But, we would at least have four or hopefully eight years of demonstrating that widespread carry does not lead to blood in the streets, and actually improves public safety. And, we could work for a legislative solution in that time.
Need to take Trump’s constitutional common sense a bit further. Mandatory, age appropriate, fire arms training in all public schools, K-12. No travel by public transportation with out presentation of firearm and certificate of proficiency. Exceptions for the infirm, incompetent and prohibited.