The pattern in the RealClearPolitics average of national head-to-head polling since March 1 has been consistent: Hillary Clinton surges to a 5-to-10-point lead; Donald Trump then closes the gap.
The speed of Clinton’s rise and Trump’s fall isn’t necessarily consistent, nor is the period over which the sine curve unfolds. In the first bulge, Clinton reached her peak lead in 21 days and the lead was gone after 81. The second time, Clinton’s peak came in 33 days and the lead was gone in 63. The third time, the most recent time, Clinton peaked after 13 days — thanks to the conventions — Trump reeled it back in over the course of 53 days.
That’s assuming that what we’ve seen in new polling represents the start of another boom-bust cycle. New polls released over the past 24 hours from McClatchy-Marist (Clinton plus-7 in a two-way race and plus-6 in the four-way) and the AP-GfK (Clinton plus-6 in both) suggest that the Clinton lead may be widening once again. Or, at least, it has widened over the past week.
So let’s assume for the moment that the pattern is repeating itself, that the Clinton convention bubble — bulge number three — is over, and a new one is starting. This may not be a fair assumption at all, but let’s assume it is. The inevitable question is: Why now? And, by extension, why did the past bubbles swell and fade?
The first bubble, starting at the beginning of March, started after a period of relative stasis in the head-to-head race. Clinton’s lead had been between 2 and 5 points, give or take, since October. Then in March her lead swelled. It corresponded with Ted Cruz’s surge in the polls, and in head-to-head polling, Clinton got more support from Democrats during her rise than Trump did from Republicans (85 percent to Trump’s 74 percent) according to Huffington Post Pollster. During the fade, that margin was narrower, a 5-point difference.
The pattern has been similar in the other two bubbles. The margin by which Democrats prefer Clinton to the support Trump gets from Republicans is larger while Clinton’s lead grows and smaller as it fades. The extent of those differences varies, but the pattern is consistent.
Is that entirely descriptive? Are Clinton’s leads mostly driven by how much Republicans like Trump and how much her own party likes her? And, if so, what causes those variations?
And why now? What is it about this past week or two that has reversed Trump’s recent improvement?
We tend to look at weird little incidents — Clinton fainting, “deplorables,” whatever — as markers that indicate the shifts in polling, but it’s often hard to pin down on thing as having made a huge difference. One thing that’s worth noting is the dashed line on the first graph, the one that averages how much support the two candidates are getting. That line has been fairly consistent: During the first and third bubbles it was around 44 percent; during the second, 43. (Both candidates saw a little less support from their own parties during that second bubble, which is likely part of the reason why that figure was lower.) What this suggests is that about 10 or 12 percent of the electorate is consistently undecided in the race, or unwilling to commit to one candidate or the other.
That’s higher than we’ve seen in past elections. In 2004, 2008 and 2012, the percentage that hadn’t committed to one of the major-party candidates by now was around 7 or 8 percent.
RealClearPolitics hasn’t been tracking the four-way race as long, but we can look at how things have changed since the peak of the second bubble. Gary Johnson and Jill Stein have polled fairly consistently, at a combined 11.4 points on average. The most that’s deviated was a point or two.
So the deviations in support for Clinton and Trump aren’t necessarily people going to one of the third party candidates.
It’s possible that support from Republicans for Trump drives a lot of what we’re seeing. That Cruz support rising in March alongside Clinton doing well — and then falling as Trump wrapped up the nomination. Clinton hammering Trump at the conventions and making Republicans wary of his candidacy — then Trump slowing rebuilding that base. Perhaps Clinton’s deplorables line helped widen that rift once again? Since the end of bubble three, Clinton’s averaging 84 percent support from Democrats to Trump’s 79 percent from Republicans. It would help explain Trump’s biggest surge in support and biggest lead: Right after his party’s convention.
The underlying question here is how Trump can expand past his peak in the polling average. He’s never polled higher than 45.7 percent, on average, a mark that Clinton has exceeded on 60 percent of the days since March 1. Trump has led for only eight days since then, never by more than 1.1 points. Can he do better? Can he firm up his base?
Or are we entering another bubble period, one that may not fade away again until it’s too late for Trump’s candidacy?