As I discussed with Bob earlier, it could be argued that he failed to protect our nation from Russian attacks on our Democratic institutions, or respond forcefully to such attacks.
It could be argued that he should have done more, but he certainly did respond to these reports of Russian interference. Here is one summary:
https://www.npr.org/2018/07/15/6292...tion-respond-to-election-interference-by-russ
I am very sympathetic to Obama's attempts to tread very carefully, First the precise breadth of these attacks and their connections to Russia took some time to fully establish. They still are under investigation. Caution seems appropriate. But even more so I suspect that Obama was deeply concerned about having the Republicans treat any investigation of Russian interference as an unethical, purely political attack on them. Particularly given the close associations between the Trump campaign and the Russian interference. I don't have to imagine these accusations: look at how Trump and some of the Republican leadership has portrayed the investigations that have taken place both before and after the election as despicable, immoral, illegal, politically driven mudslinging etc. Investigation of Russian interference inevitably meant investigating the relationship of these Russian actions to the Trump campaign; a political minefield during an election year.