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 that 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).1 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 …