Paul Manafort is going to jail.  He made millions of dollars working as a consultant to a pro-Russian Ukrainian political party and didn't pay a dime in federal taxes.  In fact, he sought to hide his money through an elaborate shell game of dummy corporations.

But there has always been a question about why special counsel Robert Mueller was so interested in him.  He is not being charged with any crime related to "Russian collusion" with the Trump campaign.  For that matter, no one charged in the Muller probe so far is being accused of collusion with Russians to swing the election.

Manafort sought to squash his indictment by claiming in a civil suit that Mueller did not have the authority to investigate his money-laundering and tax evasion.  His defense team claims that Mueller's powers to investigate went only as far as looking into matters directly related to Russian collusion.

But yesterday, the Department of Justice revealed for the first time the reason for Mueller's intense interest in Manafort.  They believe he acted as a "back channel" from the campaign to Russian leaders, thus facilitating the collusion.

Bloomberg:

"He had long-standing ties to Russia-backed politicians," Dreeben told Jackson.  "Did they provide back channels to Russia?  Investigators will naturally look at those things."

Prosecutors hadn't previously used such explicit language to describe their suspicions about Manafort.  In a previous court filing, Mueller also cited business ties between Manafort and the Russian oligarch Oleg Deripaska.

Any investigation of links between Russia and the Trump campaign "would naturally cover ties that a former Trump campaign manager had to Russian-associated political operatives, Russian-backed politicians, and Russian oligarchs," prosecutors said in an April 2 filing.

"It would also naturally look into any interactions they may have had before and during the campaign to plumb motives and opportunities to coordinate and to expose possible channels for surreptitious communications," prosecutors wrote.  "And prosecutors would naturally follow the money trail from Manafort's Ukrainian consulting activities. Because investigation of those matters was authorized, so was prosecution."

At Thursday's hearing, Downing argued that he was challenging whether Mueller "had the jurisdiction and the authority to conduct the investigation."  He focused on Mueller's release of a memo dated Aug. 2, 2017, and signed by Deputy Attorney General Rod Rosenstein, that  spelled out the reasons for pursuing Manafort.  Heavy redactions in the public version make it hard to tell all of the reasons.

This appears to be the crux of Muller's case for collusion: that Trump's campaign chairman knew a lot of Russians in and out of government and had the opportunity to direct some sort of collusion with Moscow.

But would collusion with the Kremlin be the only reason Manafort would look to establish back channels between the Trump campaign and Moscow?  Of course not.  The Trump campaign no doubt had several back channels to other countries.  This is not only legal.  It makes good sense.  Establishing personal lines of communication with other important nations would prove to be invaluable for any new president taking office

Does anyone doubt that the campaign of a former secretary of state would have had back channels to any number of countries, including Russia? 

Context is also important.  Before Russians were accused of interfering in our presidential election, Democrats, especially, were eager to establish good relations with Putin.  Barack Obama won an election in 2012 mocking Mitt Romney, who said in a debate that Russia is our number-one enemy: "The 1980s are now calling to ask for their foreign policy back," said the president.

Four years later, that statement had gone down the memory hole along with the Democrats' enthusiasm for Russia.

I guess Mueller had the authority to investigate Manafort's ties to Russians.  But his dot-connecting is flawed.  Unless he gets specific proof that Manafort's contacts in Russia were to facilitate communication with the Trump campaign in order to collude to hand him the election, Mueller will have nothing.

And that's been the big story of this entire investigation.