Even if US refineries were designed for US oil to keep domestic prices low one would have to introduce export restrictions because oil is a global commondity. Big oil will not be happy about that and it seems they have a great influence over the respublican party and Trump.
Nationalization doesn't define who is in charge though. You can have the state taking over industry, you can also have industry taking over the state. Both ultimately lead to nationalization of the industry.
