My guess is feckless Sessions wants redemption.
Political redemption.
As others here have pointed out, Sessions was very comfortable in the D.C. Senate Club.
He was a disaster as Attorney General. Now that General Flynn has been cleared, and the Acting Director of National Intelligence (Grenell) released documents, the attempted coup and the facts thereof are only going to become more and more public.
The attempted coup against Trump, followed by the Russian Hoax and persecution of the President and his associates was and is the biggest political scandal in American history.
And it grew and expanded on Session's watch. And, he knows it. He was a coward, and he knows that too.
Sessions figures if he can get back into the D.C. Senate Club, he will be with his old buddies on "both sides of the aisle" again. Maybe he will get one of his old Committees back and can be called "Mr. Chairman" again in the Senate elevator?
Sessions figures that the President will have to make nice with him, and come begging for his vote on budgets and Senate votes on legislation.
Then, Jeff will have redeemed himself, and his cowardice will all be in the past.