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In between the second and third rounds of Democratic presidential debates, Americans – particularly those in Iowa – are still learning about the myriad of candidates on the campaign trail.

Debates take on an added importance in such a crowded field as it provides the most high-profile opportunity for lower- and mid-tier candidates to have a “breakout” moment in front of a large audience. The frontrunners, meanwhile, get a chance to make their case to the country and try to escape from the debate stage unscathed.

Those moments can help jettison a mid-tier candidate into the upper strata of candidates, which is what appeared to happen in June with California Sen. Kamala Harris.

In the first Democratic debate, Harris got a huge boost after she called out former Vice President Joe Biden on some of his past policies. According to a poll from Quinnipiac University before the first debate, Harris was receiving around 7% support among Democrats and Democratic-leaning independent voters. In the week after the debate, her support surged to 20%.

But immediately after, given another couple of weeks, she dropped back down to 7% – back to where she was before the first debate.

So while going after Biden helped her momentarily, she eventually saw a drop in her support. Harris benefited from a post-debate bump that moved her into the upper tier of the race, but she couldn’t hold on to the level of support she saw in polls immediately following that June contest.

It’s hard to find patterns for any debate bumps – for every example of a candidate crashing after a big gain, there are just as many of a candidate moving with upward momentum. Or vice versa – there are plenty of examples of frontrunners who underperform and take a hit, but bounce back in the next week.

In reality, most of these bumps are temporary. Lots of candidates see a change in their polling immediately after a debate, for better or for worse, but eventually return, with less of an impact than originally thought. It’s important in moments of drastic poll changes to remember that the numbers will probably change again before voting begins, and polls are meant to be snapshots in time, not predictions.

One such example from the 2020 campaign – who saw a large change in his numbers from before and after the first debate – is Biden.

Before the debate, in Quinnipiac’s early June poll, Biden received 30% support among Democrats and Democratic-leaning independent voters. He dropped down to 22% in the week after the debate, recovering back up to 34% in late July.

Harris’ attacks seem to have hit Biden a little, and he came back – something experienced by the man Biden has targeted more than any other while on the campaign trail in 2019: President Donald Trump.

Trump lost support in CNN/ORC’s polling conducted right after the second Republican primary debate on September 16th, 2015. Beforehand, 32% of Republicans and Republican-leaning independents said they’d support him. Immediately after, he’d dropped down to 24%, but recovered a few percentage points in the coming weeks. While Biden returned to his previous polling level relatively quickly, Trump’s dip took a little longer to recover from.

The 2016 Republican primary race is one of the only presidential contests that can possibly be compared to the 2020 Democratic presidential primary, solely due to the number of candidates in the race.

In that campaign, businesswoman Carly Fiorina had a Harris-like polling bump in the week after the second Republican debate. Fiorina was polling at 3% in a CNN/ORC poll before the debate and jumped up to 15% in a poll taken just a week after. Fiorina was viewed as one of the strongest performers that night, challenging Trump on his business record.

Not quite a full month later, she was back down at 4%.

So while Harris was polling better than Fiorina to start with, they both had similar patterns.

It’s still unclear if anyone will see any real support that sticks with them after the second Democratic debate. According to Quinnipiac polling taken before and immediately after the debate, Sen. Elizabeth Warren of Massachusetts saw the biggest change in her support, though it was only 6 percentage points (still statistically significant, but not as big as Harris’ in the first debate).

Warren has been one of the only candidates with a steady increase in her support since the start of the election. She started out polling at 4% in Quinnipiac’s March poll, and has been steadily increasing since then. She was stuck in the 12%-15% range from April to June, but her most recent number (21%) after the second debate, pushed her one step closer to Biden.

But will her boost stick? Her numbers look a little like now-Housing and Urban Development Secretary Ben Carson’s did at the start of his campaign. Carson was only at 4% in a July 2015 CNN/ORC poll, getting up to 19% by September of that year.

It’s notable that Warren and Carson are extremely different candidates, with much of Carson’s support driven by those who didn’t want to elect Trump. Warren’s supporters tend to focus on her policies rather than her being a direct alternative to another candidate.

It took a while for Carson to crash – he wasn’t surpassed by Texas Sen. Ted Cruz in polling aggregates until around December of that year. Cruz had been gaining momentum for some time, but Carson’s downfall was aided by a disastrous December 2015 debate performance.