Really? In my head? Well, let's start with this.
First of all, we know that Putin wanted Trump to win, and directed people to act upon this.
https://www.c-span.org/video/?c4740808/president-putin-helsinki-cspan
Secondly, his constant denial of what happened during the Trump Tower meeting and Michael Cohen's leaked statement that Trump knew about it should also be cause for concern, especially when his reasons for the Trump Tower meeting keep changing.
Oh, and don't try and tell me that collusion isn't a crime. It almost certainly is.
"Veselnitskaya later acknowledged having close connections with Russian prosecutors, and in her role as an attorney, she has counted Russian state-owned businesses and the son of a senior government official among her clients. She entered the Trump orbit based on a promise that she could bruise the Clinton campaign. Given these circumstances, was the Trump Tower meeting illegal? Perhaps. Federal law prohibits a foreign national from giving anything of value to a campaign engaged in a U.S. election. For their part, both Trump Jr. and Veselnitskaya have said she did not hand over sensitive information on Clinton. However, it’s also a crime to solicit a foreign national to give anything of value to a campaign, or even to "knowingly provide substantial assistance" in receiving something of value."
https://www.politifact.com/truth-o-meter/article/2018/aug/07/was-trump-tower-meeting-russian-lawyer-totally-leg/