Toilet handle pointing up + lever arm dipping into tank water

(Caveat: I'm not familiar with the workings of a toilet so bear with me if this is a silly question.)

The other day I noticed that my toilet's lever was pointing upwards more than it should (picture 1); opening up the tank showed that the lever was pointing down into the tank's water (picture 2). So logic dictates that the lever loosely angling down from gravity is making the handle point up.

Now, I can't figure out how to get the level to go back to the "level" position, where it and the handle would be properly parallel. I've tried tightening/loosening the nut attached to the handle and it didn't seem to change anything: the handle and lever still move very loosely regardless of how tight the nut is.

Am I missing a step to fix the existing hardware, or should I replace the entire handle/lever assembly? Thanks ahead of time.

 

There is a stop in the handle to keep the lever horizontal. That stop has broken.
You'll need to replace the arm assembly.
The handle fits into the tank thru a square hole. Make sure that hasn't moved.

The arm inside the toilet looks bent. It should be over the top of the stopper.

 

The nut on back of handle that holds assy in may be loose. If it is handle will slip by stop. Inside lever still looks bent.

 

I think the bent lever is just a trick of the photo; if I even-out the handle so it's parallel to the ground, the lever is too.

@pugs - Already tried tightening the nut, no effect.

@ PJmax - It makes sense that the stop would be broken, since I don't think I can see that from the exterior. Everything else seems fine.

I'll go ahead and replace the whole assembly, thanks to both of you.