Joy Reid opened this segment today with this Trump clip:

"I will tell you this, Russia, if you're listening, I hope you can find the 30,000 emails that are missing. I think you will probably be rewarded mightily by our press. Let's see if that happens. That will be next."

"Well, that particularly memorable shout-out to Russia regarding Hillary Clinton's emails is now raising the question of what did Donald Trump know and when did he know it?" Reid said.

"NBC News learned that Robert Mueller is asking witnesses if Trump knew that Democratic party e-mails were hacked before the public did. And whether he was involved in their strategic release by Wikileaks. Is this the beginning of the case for collusion?"

"Let's start with NBC News reporting about Trump's shout-out to Russia about the missing emails. Witnesses have been asked whether Trump himself knew whether John Podesta had already been targeted. They were also asked if Trump was advised to make the statement about Clinton's emails from someone outside his campaign, and if the witnesses had reason to believe Trump tried to coordinate the release of the DNC emails to do the most damage to Clinton," she said.

She asked former prosecutor Paul Butler if we've seen any evidence "that has given us an answer on whether Trump had advanced knowledge of what Wikileaks had done when he made that shout-out to russia."

"Yes, we have," he said. "It's been clear for a long time that Trump tried to impede the investigation of Russian collusion. The question is why. This week, we learned the answer, because he was trying to collude with the Russians. so now the question is, did he cross the line with 'it would be a nice thing, if you help me win the election,' to the illegal act of conspiring to defraud the United States. We look at the timeline, the answer is yes. Again.

"In April, George Pappadopoulos gets information, and then Trump saying, Russians, if you have knowledge. Then we have this release of dirt on Hillary that the Russians have. It looks like he was coordinating it," Butler said.

"In the past we had this debate about collusion," Reid said. "I want to play this clip of June 24, 2016. Lester Holt in that famous interview with Donald Trump specifically talking about the question of the emails and the hacking of the Democratic party. Take a listen."

LESTER HOLT: You also made the claim that her email, personal email server had been hacked.

TRUMP: Her server was easily hacked by foreign governments.

HOLT: Suggesting that as --

TRUMP: You don't know that it hasn't been.

HOLT: But suggesting she could be compromised as president what. What evidence do you know that it was hacked?

TRUMP: I think I read that, heard it. Someone had given me that ...

Mueller may not have a smoking gun just yet, but if he doesn't, he's very close.