Where Clinton's Post-Convention Bounce Didn't Measure Up

That whole likability thing? Still an issue.

Andrew Harnik / AP

Every presidential candidate expects their polls to look pretty good after they accept their party’s nomination. After all, a convention is a week of positive coverage that concludes with a balloon drop—what’s not to like? (And the opposing party’s customary cease-fire doesn’t hurt, either.) But for the oh-so-cynical among us, this temporary boost is the political equivalent of a participation medal—the candidates showed up, they accepted the nomination, they got three percentage points. Big deal.

That said, poll nerds are watching closely to see if Hillary Clinton’s honeymoon will outshine (or outlast) Donald Trump’s.  So far, it’s looking likely. According to Real Clear Politics’ rolling average, Trump jumped ahead by 3 percentage points after the Republican National Convention,  briefly topping Clinton. But the former secretary of state has come into her own.  Clinton more than made up her lost ground with voters amid the post-Katy Perry bliss, surging by a net of 5.5 points and leading Trump 46.4 percent to 42 percent.

This doesn’t tell the whole story. Most folks are paying attention to head-to-head polling between Clinton and Trump, also known as the horse race. That’s a zero-sum game; whenever Clinton surges, Trump falters, by mathematical necessity. I’d argue this magnifies post-convention swings.

Why not look at how well-liked a candidate is on their own merits, instead of in comparison to another politician? Most polls have a “favorability” prompt that gets at this question. While it’s not exactly the same measure—pollsters are asking voters how much they like a candidate, not how much they want them to be president—I’d still expect to see a similar statistical bump after a convention. And since a voter can think favorably of any number of candidates (heck, they might like all of them), a positive score for one won’t necessarily mandate a negative score for another.

Charting this measure tells a bit of a different story for Clinton in the week since the DNC. If we take each candidate’s net favorability score—the percentage of voters who like them, minus the percentage who don’t—on the first day of their respective conventions and set that as the baseline, here’s the curve that results:

Trump’s likability surged quickly in the days following his nomination, to a degree his rank in the horse race did not. While his numbers have since come to Earth—weighed down, no doubt, by his unpopular and public feud with the grieving parents of a slain soldier—he spent nearly two weeks flying high.

By this measure, Clinton currently disappoints. She’s a little over a percentage point behind where Trump was at the same time, and her favorability hasn’t risen as quickly. That said, slow and steady wins the race: Trump had stalled out by this point in the week, and Clinton’s stock is still rising. (The shifts shown on the graph are probably off by a few days; most polls are conducted over several days before being released publicly.)

Compare this with Barack Obama in 2012, whose popularity shot up after the convention and mostly stayed there for the following two weeks. Then again, everyone’s better off than Mitt Romney, who actually polled worse in favorability following the 2012 convention in Charlotte, North Carolina.

To be clear, both Clinton and Trump are still unpopular. Only 41 percent of Americans think favorably of Clinton, and even fewer like Trump. But the Republican nominee’s burstiness should worry the Democrats. Clinton’s convention showcased some of the best speakers in the biz—Bill Clinton, Michelle Obama, President Obama himself. And Hillary Clinton’s finale wasn’t half bad. Despite that, Trump’s meandering lineup of soap stars and Republican also-rans still managed to make him more likable, at least temporarily. When he’s on, he’s on.

Post-convention poll surges are a flash-in-the-pan phenomenon. Does it matter that Trump’s flash was flashier? Perhaps not. He’s still losing the horse race, after all. But Clinton has got to keep an eye on those slow-to-rise favorability figures. Beyond his rock-solid base, Trump’s support burns off quickly. But if he turns up the heat in the week before Election Day, Clinton might not be able to keep up.