The 'burden of proof' is on the plaintiff, since the defendant is presumed innocent until proven guilty. [=the plaintiff must prove that the defendant is guilty]
The 'tax burden' has been falling increasingly on the middle class. [=middle class people have been paying a greater portion of taxes]
For the rest of his life he 'was burdened' with the knowledge that he had done nothing to help them.
(..) If you're reading this letter, I'm no longer with you and I miss you and love you always and forever. It also means I have failed and must place an awful burden on your shoulders. Lara, by now I'm sure you will have discovered the clock I concealed. The clock is the key, Lara. (..)2001 Lara Croft: Tomb Raider