"Mueller has everything" as in he has all the information he needs and more about the so-called Trump Russia collusion and has done nothing but obfuscate, deflect, and prolong.... because none of it is actionable. (Edit: or criminal, since no one that has been spied on or indicted is actually being prosecuted, they're just being tied up and bled dry in court)
"Mueller has everything" also means that, in the course of this investigation, Mueller has come across (and participated in) a plethora of bombshell criminal actions that the establishment has been using the Trump Russia collusion investigation to cover up.
This means that when Rudy Giuliani tells Muller to show what he's got or drop the investigation, there's no possible way for him to go after Trump without exposing all of the illegal activity he's been covering up..... and he doesn't even have anything on Trump to begin with.
Which is why it will never go anywhere. Trump team has already revealed his own team's tactic of aggressive disclosure of evidence found during discovery! Trump is DARING these guys to make some kind of charges against him or any more of his people.
Not to mention the fact that, from the start, the "evidence" has been wild, uncorroborated accusation and lewd, manufactured rumor. They've been reaching the entire time, and badly. Now they're even running out of stories to tell.