Hillary's a crook, who has to go to prison! Elect Donald Trump and he will appoint someone who will put her there!
This is not a new onslaught by Trump. Here he is a couple of months ago:
However, since her speech about him last Thursday, he has really exploded on this claim.
Why the sudden harping on the subject of Hillary's alleged criminality? Well, I think that something dealt with in a Daily Kos post today, about the lawsuit against Trump University, gives a clue:
"Judge Curiel denied Trump’s summary motion (to dismiss) in Low because there is a dispute over how much personal involvement Trump had, and he advertised that he did so there's evidence for Curiel to deny the motion and proceed to a jury trial. This was expected.
So on July 18 we find out whether Trump will be on trial not just for violating consumer protection laws but also for Trump University itself being a criminal enterprise, i.e. RICO.
That’s part of why Trump is trying to poison the well on Curiel, because the charges he'd be defending are so serious.
Side note: The GOP Convention starts July 18.
The judge is very likely to let the trial go forward, given the opinions of people like New York's Attorney general:
"New York's attorney general, who is leading a lawsuit against Trump University there, made his view of the case clear on Thursday: "It's fraud. This is straight up fraud...The law is very clear."
It is necessary for Trump to convince the voting populace (probably impossible, but whatever...) that the case against his sham university is nothing but a political smear, along the lines of, well, the hundreds that the Republicans have conducted against Hillary the last couple of decades. One way to do this is to deliberately insist over and over again that the judge is politically biased. Another way is to insist every chance he gets that Hillary is a criminal too, only saved from prosecution for her unexplainable crimes by Democratic abuse of the judicial process. This latter tactic is, I think, his best shot- to convince millions of voters who are already deeply cynical about (Republican generated) government dysfunction, that all these charges are nothing but dirty tricks. Not a good shot, but it's all he's got, so I don't think he is going to suddenly turn into a decent human being and let justice take its course.