The battle was the Indiana primary; the war is the general election. Ezra Klein (vox.com) lists his reasons for thinking Trump will lose and what Democrats must do. Here are the first few.
On Tuesday night, the Republican Party confirmed the worst suspicions liberals had of it. Five years ago, it would have sounded like a partisan slur to say the GOP harbored enough racial resentment, xenophobia, anti-intellectualism, anti-elitism, and latent authoritarianism to nominate someone like Donald Trump. But it was true.
Credit where it's due. The Republican Party is what congressional scholars Thomas Mann and Norm Ornstein said it is: "ideologically extreme; scornful of compromise; unmoved by conventional understanding of facts, evidence and science; and dismissive of the legitimacy of its political opposition." In case you are skeptical of that final charge, recall that Trump began his rise in the Republican Party as a champion of the birther movement.
Donald Trump tends to trail Hillary Clinton by about 10 points in general election polls — a landslide in contemporary American politics. "There have been 10-point shifts over the general election season before, even if it’s uncommon," writes Nate Cohn, the New York Times's resident polling wonk. "But there isn’t much of a precedent for huge swings in races with candidates as well known as Mr. Trump and Mrs. Clinton. A majority of Americans may not like her, but they say they’re scared of him."
The result is Hillary Clinton is a weak candidate in a commanding position. Her favorability numbers trail far behind what Barack Obama enjoyed at the outset of the 2008 election — he hovered around 55 percent, while she barely clears 40 percent — but her potential vote share far exceeds anything he could plausibly have hoped for. It is possible Trump could lose in a Goldwater-like landslide in a way that was not possible for McCain
... Trump offers an opportunity to Democrats: if they can manage to hold their left flank while attracting a few percentage points worth of disgusted independents and moderate Republicans, they can consign the GOP to minority status for the foreseeable future — much as happened to the California Republican Party after Pete Wilson. The difficulty for Democrats is that such a strategy requires ideological and tonal moderation even as the weakness of Republicans emboldens liberal groups to demand more ambitious policy and the extremism of the Trumpism calls forth an angry, fearful response from the Democratic base.