The special counsel just basically accused President Trump's former campaign chairman of trying to get witnesses to lie to protect him.

Now, Paul Manafort could be in a host of legal trouble on top of the issues he already faced. Prosecutors are asking a judge to consider putting him in jail for the next few months rather than keep him under house arrest as he awaits two trials this summer.

That should worry Trump for two reasons:

  1. The more legal pressure there is on Manafort, the more pressure he'll face from Robert S. Mueller III to sign a plea deal. Any plea deal would likely offer Manafort a reduced jail sentence in exchange for sharing what he knows about the investigation into whether the Trump campaign worked with Russia to win the 2016 presidential election.
  2. Besides the president or his family, there is no bigger fish in the Russia investigation than Manafort. It's not clear exactly what Manafort knows, but he does appear to be a crucial linchpin between Trump's campaign and Russia.

Manafort has until Friday to respond to the allegations. Mueller has seemed particularly focused on Manafort — and particularly willing to apply pressure — from the start. Last summer, the FBI raided Manafort's home unannounced before dawn. As I wrote then:

In many ways, Trump's former campaign chairman is squarely in the crosshairs of the Russia-Trump collusion investigation: His brief tenure as the head of Trump's campaign happened as concerns about Russia's meddling in the 2016 election were heating up, he's got high-level connections to Russia in his own right, and he's got a whole host of scrutinized financial dealings that could make him a useful tool for investigators seeking cooperation.

Manafort likely has knowledge of the inner workings of the campaign, Jeffrey Jacobovitz, a white collar defense lawyer who has represented members of the Clinton administration, told The Fix after that raid.

Plus, Manafort was in that meeting in Trump Tower, the one that legal experts have said may have crossed the line into conspiracy.

Donald Trump Jr. was told the Russian government was asked if he wanted to meet a Russian lawyer who had dirt on Hillary Clinton. Trump Jr. said yes, and brought along Manafort as well as Jared Kushner, Trump's son-in-law.

Manafort took notes of that meeting, and those notes could be key evidence if there are any collusion-related charges.

Finally, of all the Trump campaign officials, Manafort has the most known connections to Russia. Before he joined Trump's campaign, he was a political consultant in Ukraine, where he helped elect a president backed by Russia.

And the FBI accused the Russian manager of Manafort's lobbying office in Ukraine of having ongoing ties to Russian intelligence, though Konstantin Kilimnik has denied that.

The Washington Post's national security reporters read between the lines of court documents filed Monday against Manafort, and they found strong hints Kilimnik may have helped Manafort reach out to two unnamed witnesses to ask them to falsely testify about where his lobbying work took place.

That lobbying work happened before the Trump campaign, but it isn't just tangential to the Russia investigation: It's now central to it. In October, the special counsel charged Manafort and his business associate, Rick Gates, with money laundering and making false statements related to that lobbying in Ukraine.

Gates reached a plea deal in February in which he pleaded guilty to just two of more than a dozen charges. But Manafort has so far resisted, vowing to fight all charges. He even tried to get a court to throw them out, arguing they weren't in the parameters of the Russia investigation.

Fighting for his innocence could get a lot more difficult for Manafort now.

His alleged tampering suggests he does have something to hide from prosecutors. That gives Mueller an opening to keep applying pressure in the hopes Manafort will start cooperating with his team.

That's not a comfortable position for Manafort to be in, and it's certainly not a comfortable one for Trump, either.