This post, originally published in August 2017 after news the FBI raided Manafort's home, has been updated to reflect the latest news.

Paul Manafort isn't on trial for his Russian connections in the context of working to get Trump elected. Or is he?

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 overlapped with concerns about Russia's meddling in the 2016 election, he's got high-level connections to Russia in his own right, and he's a key link to the president as one of the highest-ranking Trump campaign officials ensnared in the investigation.

Manafort's legal team unsuccessfully tried to get the financial-related charges he's facing on Tuesday thrown out, arguing his past work as a lobbyist in Ukraine has nothing to do with the Trump campaign and Russia. But the justice system disagreed. Manafort goes on trial in Virginia on charges of hiding money to avoid paying U.S. taxes from his days lobbying in Ukraine. He's facing a second trial on similar charges this fall in D.C. Here's why Manafort's seemingly unrelated trial could be very related to the Trump campaign and Russia.

1. He was Trump's campaign chairman for several key months in 2016. Besides the president or his family, there is likely no bigger fish in the Russia investigation than Manafort. He was aware of the inner workings of the campaign for several key months when Russia seemed very prominent in the U.S. political news. He was the head of Trump's campaign around the time Democratic emails allegedly hacked by Russians got dumped into the public sphere, for example.

2. He was in *that* meeting. When Donald Trump Jr. was told the Russian government was trying to help his father win, and oh by the way, do you want to meet with a Russian lawyer who has dirt on Hillary Clinton, Trump Jr. didn't go alone. He brought along Manafort and Jared Kushner, Trump's son-in-law.

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

That meeting's circumstances are “as close as you can get to a smoking gun” on whether the Trump campaign colluded with Russia, white collar lawyer Jeffrey Jacobovitz and other legal experts told The Fix last summer when news of the meeting broke.  Now a key question heading into Manafort's trial is whether the president himself knew about the meeting. Trump's former lawyer and fixer, Michael Cohen, recently alleged just that. Trump has denied it.

3. He's got lots of ties to Russia. A Russian aluminum magnate. A pro-Russia former Ukrainian president. A Republican congressman who advocates for close ties between the United States and Russia. A business associate from his time in Ukraine who once served in the Russian army and had dinner with Manafort during the campaign. Most recently, 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.

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.

His Russia ties helped end his official work with Trump, too. During the campaign, the New York Times uncovered ledgers in Ukraine for secret, under-the-table payments to the pro-Russia party's allies. Manafort's name was in them, though he denied any wrongdoing. The news eventually led to Manafort's resignation from Trump's campaign, three months after he was elevated to the top job.

4. Investigators could use him as leverage.  The judge presiding over Tuesday's case thinks this trial is a way to squeeze Manafort into sharing what he knows. As he allowed the case to continue, the judge said special counsel Robert S. Mueller III wants to make Manafort "sing" about Trump.

Threatening someone with legal trouble is a common tactic to try to get them to cooperate with the broader investigation, Jacobovitz said. Manafort's business associate, Rick Gates, faced similar charges to Manafort's and pleaded guilty in February to just two of them, agreeing to help investigators with what they want to know about Manafort.

It's possible Manafort could lead investigators up the Trump-campaign food chain if he agrees to a similar plea deal. At the very least, the symbolism of his trial is powerful. Manafort is the highest-ranking Trump campaign official to get indicted in Mueller's investigation.

For all these reasons, Manafort was also the perfect target to send a message to the rest of Washington, said Jack Sharman, a white-collar lawyer in Alabama and former special counsel for Congress during the investigation into President Bill Clinton during the Whitewater case. He talked to The Fix in August after the FBI raided Manafort's home, unannounced, before dawn. And that message was: The special counsel investigation means business, and isn't afraid to target high level members of the Trump campaign.