What does the idiomatic expression still riding a deadhorse mean?

The idiom "still riding a dead horse" means to continue to argue or debate a point that has already been settled or is no longer relevant.

It's like beating a dead horse – the horse is already dead, so there's no point in continuing to hit it.

Here are some examples of how it might be used:

* "We've already discussed this issue for hours. Let's not ride this dead horse anymore."

* "The company decided not to pursue the project, so there's no need to keep riding that dead horse."

* "The argument has been resolved, so please stop riding this dead horse."

The idiom highlights the futility of continuing a discussion that has reached a dead end. It suggests that it's time to move on and focus on other issues.