The past is prologue.

The Republican primary contest was not just tough. It was a battle for the soul of the party, fought to the bitter end, by opponents who feared that Mr. Trump would rupture their movement and betray their ideals. On Wednesday, Mrs. Clinton’s campaign harvested those angry months for a montage of criticism: a video of attacks on Mr. Trump during the primaries from respected Republican leaders — including Mitt Romney, the party’s nominee in 2012, and Senator Lindsey Graham of South Carolina — describing Mr. Trump as dangerous and unprepared to deal with world affairs. Expect to see more of these clips in the fall.

Are Republican voters in play? Democrats think so.

Along with the videos of Republicans, there were paeans to faith and to the strength of the United States military, contrasting Mr. Trump’s remarks about the military’s decline. There was a full-throated endorsement of Mrs. Clinton by former Mayor Michael R. Bloomberg of New York, once a Republican and now an independent, who emphasized his disagreements with the Democrats on education and spending issues. And there was Mr. Obama himself, an unpopular figure in Republican circles, seeking to undermine Mr. Trump’s partisan credibility. “What we heard in Cleveland last week wasn’t particularly Republican — and it sure wasn’t conservative,” Mr. Obama told a prime-time television audience. Those moments suggested that Mrs. Clinton believes Mr. Trump is toxic or unconventional enough for her to peel off a significant slice of Republican voters.