Seneca, South Carolina (CNN)Ted Cruz is calling Donald Trump's bluff.Cruz slammed Marco Rubio and Donald Trump during a dramatic press conference Wednesday that underscored the escalating tension among Republicans ahead of Saturday's South Carolina primary. But it was his broadside against Trump that sounded like a challenge: sue me."I have to say to Mr. Trump you have been threatening frivolous lawsuits for your entire adult life," Cruz said at a press conference in South Carolina. "If you want to file a lawsuit ... file the lawsuit."He said Wednesday said that Trump's lawyers have sent his campaign a cease and desist...