I think it is as simple as Pres. Trump doesn't have a lot of patience for people who don't fight. AG Sessions should never have recused himself. Now that he has and the Russian probe has led to a special prosecutor Pres Trump wants the Rats to feel the same heat. I don't blame Trump for wanting to fight. The Pubs always want to be "gentlemen" and "follow the law" and then lose.
I don't think this true.
Sessions had to recuse himself.
The investigation started by looking into the Russian interference into the election, and the campaigns.
Trump really didn't have this massive organized campaign structure, like traditional candidates do, and Sessions took on a larger role than he may have during a tradition campaign.
If Sessions doesn't recuse himself, he would be in charge of an investigation into an election he was quite involved in.
It would have looked as if were trying to control the outcome, to his own benefit.
Everyone would have had a fit.
It would have had the appearance of Sessions investigating himself.