Donald and Melania Trump on stage at the Republican National Convention

Melania Trump’s stunning plagiarism at the Republican National Convention should by all rights be fatal to her husband’s campaign for president, not merely because she plagiarized but because of who she plagiarized from. Melania, who claimed beforehand that she wrote her speech "with as little help as possible," stole from none other than Michelle Obama, whose family has been the target of the right’s most bitter hatred and ridicule for a decade now.

Donald Trump has argued again and again that Barack Obama is an incompetent danger who is trying to drive the country aground, yet it’s the words of Obama’s own wife that the Trump family has seen fit to appropriate as its own. Those two things are impossible to square. If the Obamas are so odious and hazardous, how could their values be worth adopting? Or to reverse the equation, since the Obamas’ values are so evidently worthy of adoption, as Melania demonstrated through her theft, then the case against the Obamas falls apart.

The particular passage that Melania chose to lift makes her transgression all the more devastating. Michelle Obama spoke eloquently about working hard and treating others with respect and dignity. “Your word is your bond," she said—and so, in an extraordinary irony, did Melania repeat after her. If you copy without attribution a passage about hard work, dignity, and your word being your bond, then you lack all dignity yourself.

Donald Trump did not speak these words himself, but he cannot disavow them. He personally introduced Melania on stage before she spoke, and the very purpose of her address was to promote an image that her husband wants to see promoted. Indeed, in a statement, Trump’s campaign stood behind Melania’s speech and refused to acknowledge any plagiarism.

So how can Trump go forward now, after admitting that the Obamas’ values are his values? He cannot—he simply has no argument left to make.