One of the big questions heading into the Democratic National Convention late last month was whether Hillary Clinton could rally Bernie Sanders supporters to her side. Before the convention, many Sanders supporters said they would support Clinton in a two-way matchup against Donald Trump, but when pollsters offered them third-party candidates as an option, they abandoned her.

Then, on the first night of the convention, Sanders gave his big speech urging his voters to support Clinton, and we can now see that the convention did help persuade some Sanders voters to switch. But about a third of Sanders’s voters are undecided or still going with a third-party candidate when given the choice.

Before we get to all the data, let’s be clear about what we’re discussing: The Sanders holdouts aren’t that large a group. If they were forced to choose only between Clinton and Trump, the vast majority would choose Clinton and yet they would add only about 1 percentage point to her overall margin over Trump, according to current polls. That could matter in a close election, but the election isn’t looking all that close at the moment.

The conventions did move some Sanders voters to Clinton. In national polls taken right before the conventions, Clinton was winning around half of Sanders supporters when Gary Johnson and Jill Stein were included as an option — 57 percent (per CNN and Marist) and 44 percent (per YouGov). Now, Clinton is at 69 percent (CNN), 65 percent (Marist) and 49 percent (YouGov).

Without third-party candidates, Clinton was already doing much better with Bernie’s fans. Still, the convention helped: She moved from 79 percent up to 91 percent among Sanders supporters in CNN’s polls, 68 percent to 75 percent per Marist, and 59 percent to 65 percent in YouGov’s surveys.

But the sizable portion of Sanders supporters defecting from Clinton when given other options could still be a problem for the Clinton campaign if the election tightens.

WITH THIRD PARTY WITHOUT THIRD PARTY POLLSTER CLINTON TRUMP CLINTON TRUMP DIFF. IN CLINTON’S MARGIN CNN 69% 3% 91% 6% +19 Fox News 68 7 79 10 +8 Marist 65 5 75 6 +9 YouGov 49 9 65 14 +11 Average 63 6 78 9 +12 Sanders supporters are still more likely to back Clinton without third-party candidates All percentages are rounded. CNN, Marist and YouGov asked about Clinton, Johnson, Stein and Trump when third party candidates were included. Fox News only asked about Clinton, Johnson and Trump.

Pollsters show Clinton receiving varying levels of support from Sanders voters, but CNN, Fox News, Marist and YouGov all show Clinton’s margin over Trump among these voters shrinking when third-party candidates are presented as options. On average, Clinton loses 12 percentage points off her margin over Trump among Sanders backers — identical to the change I calculated before both conventions took place. Clinton is below 70 percent among Sanders backers in all four polls and wins an average of just 63 percent when third-party candidates are included. That’s about as well as Trump is doing among well-educated, moderate Republicans — the wing of the GOP least likely to back him. In other words, the Democratic convention seems to have been somewhat of a failure in convincing Sanders voters who oppose Trump to consolidate behind Clinton rather than Johnson or Stein.

Of course, Clinton has already won over some Sanders holdouts, and she may just steadily pick up more of their votes as the campaign progresses. Additionally, Johnson’s support in national polls — in both our polls-only and polls-plus forecasts — has been trending downwards slightly. That suggests voters may be moving away from third-party options, which is in keeping with the history of third-party candidates fading as the election nears.

The better news for Clinton is that none of this may matter in the end. As I mentioned, getting these wayward Sanders backers on board would only marginally help her. And she leads nationally by 6 or 7 percentage points at the moment. She may not need their help.





FiveThirtyEight: On the ground at the Democratic National Convention