So how exactly did Joe violate section b(2)?Here's the bribery statute if it will help. I'd refer you to section b(2). The evidence you are asking for is not required by the statute.
18 U.S. Code § 201 - Bribery of public officials and witnesses
www.law.cornell.edu
B
(2)being a public official or person selected to be a public official, directly or indirectly, corruptly demands, seeks, receives, accepts, or agrees to receive or accept anything of value personally or for any other person or entity, in return for:
(A)
being influenced in the performance of any official act;
(B)
being influenced to commit or aid in committing, or to collude in, or allow, any fraud, or make opportunity for the commission of any fraud, on the United States; or
(C)
being induced to do or omit to do any act in violation of the official duty of such official or person;