Conventions are not complicated things. They are a few nights' worth of free media attention, during which each political party can make its best case to voters for the general election. There's lots of ceremony and far, far too many speakers, but at the end of the day, it's just one long ad for a candidate — and, essentially, the only time during the campaign when this happens.

As we've noted before, Donald Trump blew it. Gallup has been tracking the response from voters to conventions since 1984, and the Republican National Convention of 2016 was the first for which more people said it made them less likely to back the candidate.

The Washington Post-ABC News poll released Sunday includes data that gives a bit more insight into just how Trump managed to make his position worse.

Before the conventions, the plurality of support each candidate received was thanks to people who wanted to vote against the alternative. In other words, most people who said they were backing Hillary Clinton were backing her because they wanted to see Trump lose, and vice versa.

After the conventions, though, that changed: A slight plurality of Clinton supporters now back her because they want her to be the president. Trump's position improved slightly — but the percentage of support he gets from people who are doing so out of enthusiasm for his candidacy is still lower than the percent who said that about Clinton before the conventions began. Before the conventions, 57 percent of those who backed Trump did so because they opposed Clinton; after the conventions, that figure was 56 percent.

The big change was with independents. Independents who supported Clinton before the conventions were far more likely to say that it was out of opposition to Trump, by a 2-to-1 margin; after the convention, support for Clinton from independents was only slightly more because they opposed Trump. In fact, independents back Clinton out of enthusiasm for her at the exact same margin that Republicans back Trump out of enthusiasm for him (45 percent of each group).

There was also a big shift in favorability ratings for Clinton after the conventions. Before, her net favorability — those viewing her favorably minus those viewing her unfavorably — was at minus-17. After, she improved to minus-6. Trump's numbers moved much less, from minus-28 to minus-25.

In this case, that change for Clinton is largely because the net favorability from Democrats improved dramatically.

Why did that happen? Because the conventions helped solidify Democrats behind her candidacy. People who supported Trump and Clinton in the primaries were always heavily likely to support them in the general election, too. But only 79 percent of those who supported Bernie Sanders in the primary contests planned to back Clinton before the conventions, compared with 86 percent after, with Trump's support among that group being cut in half. Among those who supported a Republican besides Trump in the primary, 12 percent planned to back Clinton before the conventions. After? That increased to 17 points. They backed Trump by 64 points on net before the conventions and by 57 points after.

In other words, the conventions didn't unify Republicans around Trump. The conventions made the rift in the party worse.

Part of this is certainly that Clinton's convention was successful — and that the Democrats' outreach to Republican moderates had an effect. But part of it was also clearly that Trump's convention was a flop.