Asking the DOJ/FBI to investigate the DOJ/FBI, particularly with the track record of the past year, doesn’t seem realistic unless this is a political statement. He might try declaring this some form of national security risk and have military investigators to step in.
This is all about the optics. Trump knows that public opinion plays into this and when enough GOP/independents are outraged about a Nixon like operation in the Obama DOJ/FBI..... then Congress will scream for a SP. Meantime, the US Atty Sessions talked about continues to his work.
Slow walk this thing into the summer and get hearings in August and the fall elections will be a breeze.
That’s what the long game looks like.....patience.