这么问他

Dear Applicant,

I didn't care about your IRA, but I do care about your honesty.

YOU chose to put the 20K into YOUR rental application, because of your own mis-interpretation of the application.  "I should have interpreted the question with a bit more clarity to mean liquid assets. Had I known that I would not have mentioned it." See your 3rd email.  You opened up your IRA for examination by your own action. 

Now I don't see evidence supporting all the information in your application.  Either you lied in your application, or you have to give me the evidence. Show me the $20K YOU put in your application, end of story.  

Otherwise, the application will be rejected for the reason of dishonesty.