Manafort had alerted authorities to a controversial meeting on June 9, 2016, involving Trump’s son Donald Jr., other campaign representatives and a Russian lawyer promising damaging information on Hillary Clinton, according to people familiar with the matter. The president and his son-in-law, Jared Kushner, were dragged into the matter in July as details repeatedly emerged that contradicted the initial accounts of that meeting.
Manafort disclosed the meeting to lawmakers about three months ago in response to a congressional request for any information related to Russia during his time on the campaign. He also provided more than 300 relevant documents to Congress, though he no longer had access to emails from the campaign.
Manafort’s business associates also risk being engulfed by the probe.
https://www.bloomberg.com/news/articles/2017-08-10/with-bank-subpoenas-mueller-is-said-to-turn-up-heat-on-manafort