At the heart of the effort to disqualify the prosecutors in Donald J. Trump’s election interference case is the argument that the romantic relationship between Fani T. Willis‚ the Fulton County district attorney‚ and Nathan J. Wade‚ the special prosecutor she hired‚ created a conflict of interest. That argument has been put forth primarily by Ashleigh Merchant‚ the lawyer for Michael Roman‚ a former Trump campaign official and a co-defendant in the case. Ms. Merchant accuses the district...