How safe is it to visit Tangiers after recent bombing in Morocco?
Possibly safer than it was before. I expect security will be tighter for a while, plus whatever group organized the Morocco bombing may need some time before doing anything else.
Only the US Department of State can answer that question accurately. Check with them before traveling there.
You have a lot more faith in the State Dept. than I do! I don't think they predicted the Marrakesh bombing, so why do you think they could predict the next? Nothing wrong with checking their advice, though, although I usually read the UK and Australian advice as well, the State Dept. tend to be nervous Nellies.
One random bomb is not the same as the political upheaval that's prevalent in the rest of the northern tier. It wouldn't slow me down one bit.