Hillary has to try to disqualify Trump because she loses if the election's a referendum on her

Hillary is running, too, against the reality of President Obama policies, which she promises not only to continue, but to build on. The president’s glowing appraisal Wednesday night of his time in office bore no relation to the country most Americans see—one in which health care costs more than ever, they struggle to pay the bills, and terror attacks on Western democracies are a weekly event. The state of the country might not be quite so grim as Mr. Trump painted it in Cleveland, but the mood is much closer to that grimness than to Mr. Obama’s forced optimism.

The president’s policies, which Mrs. Clinton now owns, have alienated significant tranches of voters that she needs this fall—in particular blue-collar Democrats. Coal communities are rejecting Hillary outright. Many union workers are too, whether they be Teamsters for Trump, or police officers appalled by the Democratic Party’s attacks on their profession…

Hillary is also running against her own party, which has moved left without her. She has chased after progressives, adopting one position after another from Bernie Sanders, feting Elizabeth Warren, working “progressive” into every sentence. But this week showed that her party’s liberal wing is unconvinced, still feeling the Bern. Yes, she has done some uniting in Philly, and will likely get her own bump. At the same time, 45% of Democrats who voted in the primary told that CNN pollster they still wish Sanders were the nominee.

Mrs. Clinton will continue to warn that her opponent is a threat, to try to worry voters enough that they overcome their misgivings about her. Mr. Trump can certainly make that job easier for her. Conversely, he can help his own numbers and campaign by focusing precisely on her vulnerabilities, and by presenting a stronger policy agenda of his own.