Will there ever be solid proof? If there was would we want to admit we were so badly duped? Would we admit that foreign powers influenced us?

What do we know? 

1. Propaganda and advertising exist for a reason.  It works. 
2. The Russians pushed a lot of it on behalf of Trump.
3. Trump won by slim margins in three states the Russians pushed hard in.

Those are three facts.  Read into it what you will.  

Really, we as a people need to get more resistant to advertising and propaganda.  We buy cars because of the ladies legs in the drivers seat or the scenery in the add.  We buy beer because of the waitress in the commercial we'll never meet. We are too easily influenced.