Trump attempted to remove Mueller, then asked Don McGahn to lie and say he hadn’t. He attempted to stop Jeff Sessions from recusing himself from the Russia investigation, he fired the FBI Director over the investigation, he asked his Deputy National Security Advisor to lie, and he dictated a false statement for his son regarding the June ’16 meeting with Russians.
Trump also tampered with witnesses, perhaps the most egregious acts of obstruction. See the page on Witness Tampering for excerpts on that.
See also: Mueller’s opinions on obstruction