Most unwavering Sanders supporters plan to vote for Clinton

Demonstrators make their way around downtown, Philadelphia. Photo / AP

Among the weird scenes from the first day of the Democratic convention in Philadelphia is this one.

A truck sponsored by the conspiracy-theory site Infowars toting a billboard reading "Hillary for Prison 2016" rolled up to some pro-Bernie Sanders protesters. Infowars doesn't fit neatly onto the political spectrum, but it's by no means liberal. The Sanders supporters, though, liked what they saw.

This was shortly after the Florida delegation to the convention enthusiastically booed Debbie Wasserman Schultz, the outgoing head of the Democratic National Committee - and a member of the House representing the state.

The picture that develops is of a party split by support for and opposition to Hillary Clinton. But it serves as a good demonstration of the importance of keeping anecdotal evidence in context.

Pew Research has been polling on the 2016 campaign for months, allowing it to track attitudes among voters over time. Nearly half of the Democratic electorate, 44 per cent, changed their preference over the course of the three surveys Pew conducted. About 3 in 10 supported Clinton, wire-to-wire; about 20 per cent Sanders.

Pew asked those consistent Sanders supporters whom they support in the general election. Ninety percent said they back Hillary Clinton.

That's lower than the percentage of consistent Clinton supporters who back Clinton, which isn't a surprise. It's higher than the percentage of those who had switched who now back Clinton, though only barely.

Last week, as the Republican convention was going on, Pew offered similar research about the Republicans. Of the 44 per cent of the party that never supported Donald Trump, 79 per cent were planning to back him in the general election - lower than the percentage of Sanders supporters backing Clinton, but still nearly 8 in 10.

So why so much outrage in Philadelphia? Delegates to party conventions are not normal members of political parties. Part of the objection to Clinton stems from a sense that she doesn't adhere to principles important to more-liberal Democrats.

When Gallup asked people about the importance of compromise versus adhering to key principles in 2010, Democrats were much more likely to say that compromise was important than were Republicans. Forty percent of Democrats at that point said compromise was important; half as many Republicans did. This was shortly after the fight over healthcare and at the height of the Tea Party, though. In June, Pew asked a similar question, and members of each party were about as likely to think that winning on principle was more important than finding middle ground.

That changes depending on how fervent a person's opposition to the other party is. Those who are neutral to the other party are less likely to say that their own party should get most or all of its demands in a negotiation. And those who attend a political convention, it seems safe to assume, are toward the edges of partisanship.

There's clearly some correlation to partisanship; whether or not that extends to orthodoxy between members of the same party isn't clear. We're assuming that it does.

Pew did find that more-liberal Democrats - like those who backed Sanders in the primaries - felt more coldly to Republicans than more moderate ones. This makes sense: Those Democrats would then be more inclined against compromise between the parties. While we saw a clear shift toward more-liberal voters in the Democratic primaries this year, the Democratic Party still has a greater population of moderates than the Republican Party, according to Gallup.

We noted in March that this move to the left by Democrats varies by race. Whites who identify themselves as strong Democrats are much more likely to identify as liberal than they were 20 years ago. Blacks who identify as strong Democrats haven't seen the same shift. Black Democrats were also much more likely to support Hillary Clinton in the primaries.

There are plenty of Bernie Sanders supporters who are frustrated at Hillary Clinton, and some chunk of those voters will back Donald Trump in November. Most Democrats - even those who consistently supported Bernie Sanders in the primary - plan to back Clinton. Those Democrats are more likely to be moderate and, Pew's data suggests, more willing to accept compromise.

That, it seems clear, isn't the sort of person who would applaud a "Hillary Clinton for Prison" billboard.