Two important reminders on Trump's sudden firing of FBI Director James Comey: First, Comey was scheduled to testify to the Senate Intelligence Committee about just two days from now. That hearing wasn't intended to be specifically about Russian hacking, but as part of an annual assessment of "current and projected national security threats to the United States" it was all but certain to have come up.
Second, the person who recommended Comey be fired was himself shepherded into the attorney general's office despite demonstrably lying to Congress about his own contacts with Russian officials. While Jeff Sessions' letter mews that the FBI director "must be someone who follows faithfully the rules and principles of the Department of Justice and who sets the right example for our law enforcement officials," Sessions was forced to recuse himself from investigations into possible collusion between Russian hackers and Trump campaign members due to, well, that whole lying to Congress part.
Now, in the immediate aftermath of a blistering hearing in which once again law enforcement officials again strongly hinted at possible evidence of such collusion, Jeff Sessions and Donald Trump have assigned to themselves the task of choosing the next person to carry on the Trump-Russia investigation.
Trump and Sessions are already attempting to paint that as a coincidence. Given the uproar already, that's not likely to fly.