I'm not going to throw around the T word, but Donald Jr.'s meeting with who he clearly understood to be an agent of a foreign government, for the express purpose of recieving a thing of value to the Trump campaign, was a federal felony.
Based on reading the email chain that Donald Jr. released on Twitter he, Jared Kushner, and Paul Manafort believed they were meeting with an agent of the Russian government. Campaigns will pay for opposition research, especially if it turns up dirt on said opposition, thus dirt on Clinton was a thing of value. Donald Jr. clearly believed, based on his emails to Kushner and Manafort, that he would recieve quality opposition research. Thus all three men commited a federal felony.
As a side note, Jared Kushner's failure to note his having met with the Russian lawyer he believed to be acting as an agent of the Russian government on his disclosure form for his security clearance was a seperate federal felony of perjury.
So the real question in all of this, so far as Donald Sr. is concerned, becomes, "What did the president(ial candidate) know, and when did he know it?"