For starters, the "Special Prosecutor" position is about criminal investigation, not national security or intelligence issues, period. No crimes have been alleged or evidenced.
Director James Clapper told Senators behind closed doors, on May the 8th, that there was no evidence of collusion between Donald Trump and the Russians. This is per statements made by Churck Grassley. End of story.
Third, there is no existing legislation providing for the position and funding of a "special prosecutor." Before one can be appointed, legislation for the function/office must exist. It does not.
Rod Rosenstein, Assistant Attorney General, would be the man who made such an appointment, and Rosenstein is the person who drafted a reasoned request for Comey's termination.
Fifthly, Trump has been under investigation 9 months and NOTHING, not a shred of evidence exposing collusion, has been found by either the FBI, the NIA or the CIA, per statements made by Director Clapper.
CONCLUSION: It ain't going to happen, and for good reason.
When asked, "What would it take to end your desire for the continuation of this investigation," Democrats have no answer, nothing definitive. Clearly, Dems cannot afford to answer this question. It would pervent them from saying, ?:"Well, we have found nothing YET, thus the need for more investigation."
A Special Prosecutor would garner headlines for the next four years, during the entire period of the Trump First Term. THAT is what the Dems want.
Like I keep saying, the Dems are no more patriots than they are honest. Four years from now, 70% of America will agree.