Tor + VPN makes it very difficult. You have a lot of faith in the government. They usually just go for hackers who make research papers publicly available using school and library computers.
Ross Ulbricht, Bureau of Prisons number 18870-111, also thought Tor and a VPN would protect him from the US government.
It pretty much did, until he started ordering fake IDs shipped to his house...
It might've if he didn't use his real name while posting on stack overflow. Plus, a few other lapses in security.
Read the biography of Ulbricht "American Kingpin". The author does a good job of breaking down the sequence of really stupid things that the Silk Road founder did to expose himself over time. None of them had much of anything to do with the failures of anonymity technologies like TOR. Also, as another response here mentions, ordering fake IDs online to his own home address is exceptionally fucking stupid.