Well....actually...have then call Trump. He’s the POTUS and is in charge of DOJ.
You are mistaken. Sessions is in charge of the DOJ. Trump cannot legally command Sessions to obey him. All he can do is ask. If Sessions refuses, Trump’s only recourse is to fire him. If you think the Frederica Wilson broohaha was big, multiply it by 10,000 and you’ll get the approximate media/political hysteria that would erupt upon Sessions’ firing.
Plus, the Senate has vowed not to confirm a replacement. That’s one promise they’d likely keep.