I have lost count of the number of headlines with, "Trump has finally crossed a line..." The problem is that short of openly calling for genocide, there are no more lines left for Trump to cross.
I understand the shock and outrage with each new despicable utterance from Trump. The problem is that by reacting to each new one with "this is the final one!" we implicitly pardon everything else that he said. We suggest that everything before was forgivable. We give cover to the people who still endorse him.
[just a small sample of the "crossed the line" headlines]
Sept. 20, NPR: With Donald Trump's Birther Spin, He's Crossed A Line.
Aug. 9, Esquie: The Moment You Realize Trump Finally Crossed the Line (On Trump suggesting "Second Amendment people" should kill Hillary Clinton)
Aug. 1, 2016 Chicago Tribune: Trump crosses line on Muslim patriots who balance religion, duty (After Trump attacked Gold Star parent Khizr and Ghazala Khan)
July 29, Chicago Tribune: Trump's comments on Russia cross a line (encouraging Russia to hack HRC emails)
July 6, Boston Globe: Rep. Moulton: Trump crossed line by praising Saddam Hussein
June 2, The Guardian: Donald Trump's judge-bashing crosses a line (Mexican judge cannot be impartial because he is Mexican)
Feb 8, 2016, MotherJones: Donald Trump Just Crossed a New Line in American Politics
July 21, 2015, CNN: GOP to Trump: You crossed the line (Trump said that John McCain is no war hero because he was captured)