> Trump and his associates' participation in and enabling of this Russian activity
If you want to understand more, there is a summary of "Links between Trump associates and Russian officials" in the Wikipedia article about "Russian interference in the 2016 United States elections"[0], including this section, for example:
> In the email, Goldstone said the information had come from the Russian government and "was part of a Russian government effort to help Donald Trump's presidential campaign". Trump Jr. replied with an e-mail saying "If it's what you say I love it especially later in the summer" and arranged the meeting. Trump Jr. went to the meeting expecting to receive information harmful to the Clinton campaign, but he said none was forthcoming, and instead the conversation then turned to [US sanctions against Russia]
[0] https://en.wikipedia.org/wiki/Russian_interference_in_the_20...