If degaussing didn't restore it, then I would say the tube is about to go south.
What you are seeing is a failure in the magnetic guns designed to keep the beams focused on a single phosphor. The beams are now bleeding over to other nearby phoshpors. This causes blurriness.
As a beam sweeps over a monitor it has to be focused for each step across the internal face of the tube. This is due to the arc of the tube being longer than the radius of the sweep of the beam.
Need more details?
Basically, think of it as a pendulum swinging over the floor with the goal to keep the pendulum the same distance from the floor. This requires you to move the pivot point up and down as the pendulum swings.
Your tube's pivot point has stopped moving up and down. Maybe that is a better explanation.
