If you post an assignment question on a 3rd party site and get no answers about the subject matter, is it still considered cheating?
At my university, the answer is definitely yes. The rules here clearly state that even the attempt to cheat is misconduct (e.g. bringing a device that is capable of cheating to an exam is considered cheating even if it not used/touched).
(However, if asking a question about your assignment in some forum is cheating, depends on the rules for your course/institution. In my courses, this would not be forbidden for homework assignments, for example.)
Yes. As one example of a formal policy, here is the opening definition in the CUNY (City University of New York) Academic Integrity Policy:
1.1 Cheating is the unauthorized use or attempted use of material, information, notes, study aids, devices or communication during an academic exercise.
Exact penalties will, of course, vary by institution, department, instructor, etc. In my courses, such a case on a homework assignment would result in a zero on the assignment, and a report to the school's Academic Integrity officer (who may lay out further penalties for repeat offenders). On an exam in one of my courses, this would now be an immediate failure of the course for the semester.
Yes, attempted-but-failed cheating is still unethical/immoral, though perhaps less so (?!?) than successful cheating.
Attempted-but-failed (bad thing) X is bad, but not as bad as succesful X?
Certainly attempted murder (even if unsuccessful) is a serious crime most places.
Really, how much "moral currency" do you get back by trying but failing? Sympathy points?