Without more data, serious questions about Trump’s ties to Russia remain unanswered. Those questions are not about the 2016 election. They have to do with core issues of national security.
For example, the Barr letter does not address:
Why so many people lied to investigators about their communications with Russian officials (including former Attorney General Jeff Sessions and former National Security Adviser Michael Flynn, to name two prominent examples);
Why Trump publicly lied about his negotiations with Russia to build a Trump Tower in Moscow during the campaign;
Why Trump confiscated his interpreter’s notes from a private meeting with Putin;
Why Trump is so solicitous of Putin in contrast to his antagonistic approach to American allies such as Canadian Prime Minister Justin Trudeau;