Democrats and intelligence experts from both political parties believe information that was accidentally revealed in a court filing from Paul Manafort’s lawyers could be the biggest link yet to President Trump and Russia.

Manafort, while serving as the campaign manager for President Trump’s campaign, shared political polling data with a business associate who also had ties to Russian intelligence. The disclosure occurred by accident after the court filing, which was in response to accusations that Manafort lied during his plea deal agreement with special counsel Robert Mueller, was not properly formatted to block out information meant to be redacted.