The word "demands" is inappropriate. He appoints the AG and the AG acts as a non-political entity making decisions in the interests of the Constitution and the operation of the law.
I doubt the AG will think an investigation is required. If the AG thinks there's a cause for an investigation, even if only to remove the aspersions cast by the president, it will be a quick one.
Yes, they ordered an investigation to establish if there was a reason for suspicion and probable cause to be alarmed about the Trump campaign's collusion.
Yes, they did so properly and independently.
No, it was done for proper legal and national defence reasons, not political ones.
The reason Trump is asking is because he is trying to intimidate his political opponents and coerce the Justice Department. And because his new tack is to say that he was framed, because he sees the evidence against him piling up!
He is crossing a line which grants the DoJ independence.
And yes, he likely colluded with (or sought to collude with) the Russians, as we have been learning. No further proof than Don Junior's meeting is required. And he called Trump Senior right afterwards (blocked number will be known to Mueller via the telco) to report on the meeting.
No wonder Trump is afraid that Trump Tower was wired. He realised months ago he was vulnerable to a recording of his phone calls. He must be scared that his corrupt fixer 'Kickback' Cohen recorded them too.
This is a man who relentlessly acts guilty.