Just think about what Trump’s ignorance would entail. Donald Jr. gets an email from a guy his father knows well telling him (in an almost comically overt fashion) that the Russian government wants to help him win and they have dirt on Hillary Clinton. Right there, in the real world, there is NO chance that Don Jr. doesn’t immediately run to Dad’s office and say, “Dad, holy crap, the Russians want to set up a meeting to help us!”
Remember, by this point Trump had already, bizarrely, publicly expressed his admiration for Putin (a man much richer and more powerful than Trump will ever be) several times. Meanwhile, the campaign is very short on resources and a decided underdog against Hillary. Don Jr. not telling his father that effectively Putin “really likes” him is about as likely as him spiking an email from Tiger Woods offering golf lessons or from a Victoria’s Secret model wanting a meeting to discuss doing a photo shoot for “MAGA” swag.
Even the Trump Team’s defense of the meeting exposes the utter ridiculousness of Trump not knowing about it.