Rachel Maddow just reported on a very interesting connection uncovered by the New York Times. As I understand it, the DNC reported its servers had been hacked and the very next day, Trump's son and son-in-law and campaign manager met with a Russian intelligence agent known for selling hacked e-mails. A couple days later Trump announced he had information on Hillary that he'd be releasing to the press. The following month Jullian Assange printed a bunch of stolen DNC e-mails in Wikileaks.
Therefore, even if DJT Jr and Kushner & Manafort didn't BUY the e-mails being offered by Russia, they at least TOOK A MEETING to discuss buying them.
That's collusion.