I would say it is as safe as ever.  It has never been dangerous for tourists, but there is a much more presence of police now that is keeping the scum off the street.

I recently went during the daytime and I did notice a strong police presence.  It was a light traffic day but I went around 3pm and left by 6pm.  No problems.

No. The Mexican gov't is at war with the cartels.  There is no end in sight to the violence.

As the cartels get weaker the violence actually gets worse.  That's because as leaders get killed/incarcerated the power vacuum promotes violence among those trying to "move up."

However, tourists are not in danger.  There is an unwritten rule that violence is not allowed in the ZN, on Revolucion, and in other tourist districts.

Going to TJ is safer today than it was several years ago before street lights were added in the ZN, Revolucion was widened, and other civic improvements were made.