PHILADELPHIA — The Democratic convention is over, and delegates streamed to airports and train stations on Friday morning to return home for the summer weekend. But the contrasting back-to-back political displays — Republicans met last week in Cleveland — offered important lessons about the two presidential nominees, and their parties, as they head into the November general election. Check out our takeaways:

Democrats were more polished.

Democrats are much better at staging a convention. It was visible every night over these past two weeks, in the size of the crowds, the energy in the hall, the caliber of the speakers, the celebrity of the celebrities, and the basic coherence of the messages.

In the end, Donald J. Trump delivered a rough, and at times halting, reality-television show; Hillary Clinton offered a polished Hollywood production. The next few weeks will tell how much of a difference that makes in what matters most: whether voters prefer Mrs. Clinton or Mr. Trump.

But Mr. Trump’s sloppy convention was a missed opportunity, and sent up warning flares for Republicans already concerned about his capacity to grapple with the basic mechanics of American politics.

Conventions are challenging, but so are voter registration and turnout, opposition research and fund-raising, and the increasingly sophisticated process of identifying voters through microtargeting.