Yesterday, the political press took a temporary break from making fun of Jeb Bush to monitor a Twitter feud between (the social media staff of) Hillary Clinton and Bernie Sanders over who could claim the most authentically "progressive" record—a dispute that was also briefly raised in the CNN-sponsored town hall in New Hampshire attended last night by both candidates. Sanders accused Clinton of having previously accepted the label of "moderate," arguing that "you cannot be a moderate and a progressive." The Clinton campaign responded by attacking Sanders's voting record on guns while accusing Sanders of a "low blow" in criticizing Clinton's credentials.
Fights over ideological bona fides are commonplace in the Republican Party but rare on the Democratic side. In large part, that is because most Republicans define their party as properly acting as the agent of conservatism, while most Democrats view their own party as representing the interests of one or more social groups. Democrats locked in primary battles may accuse each other of insufficient loyalty to the party, or to a component constituency within its coalition, but usually refrain from describing themselves as progressives (or liberals) or questioning the liberalism/progressivism of others.
Sanders, of course, is an ideologically-motivated politician who had previously declined to affiliate himself with the Democratic Party as a sign of his own independence from its non-liberal factions; the entire thrust of his attack on Clinton—and, by extension, much of the Democratic party apparatus itself—is based on an ideological critique. The Clinton camp, perceiving the popularity of Sanders's message among Iowa and New Hampshire voters, has gingerly attempted to associate itself with the "progressive" label even as it continues to insist that its candidate's more incremental, pragmatic approach is the best way to accomplish Democratic goals. But this is new territory for a party that is unused to publicly debating ideology as such, and it is clear that the Clinton side is wary of making statements on the topic that might prove counterproductive in a future general election.
For Sanders, the problem with getting bogged down in an ideological dispute is that many Democratic voters are unlikely to side with him. The distribution of ideological self-identification within the Democratic primary electorate in 2008, the last contested presidential nomination race, was as follows in the ten biggest states in the country, according to media exit polls:
California: 50% liberal, 37% moderate, 13% conservative
Texas: 37% liberal, 40% moderate, 22% conservative
Florida: 51% liberal, 37% moderate, 13% conservative
New York: 57% liberal, 33% moderate, 9% conservative
Illinois: 48% liberal, 41% moderate, 10% conservative
Pennsylvania: 49% liberal, 40% moderate, 10% conservative
Ohio: 40% liberal, 46% moderate, 14% conservative
Georgia: 47% liberal, 41% moderate, 12% conservative
North Carolina: 42% liberal, 37% moderate, 21% conservative
Michigan: 49% liberal, 41% moderate, 10% conservative
As we can see, self-identified liberals constituted more than half of the Democratic electorate last time around in only two of these ten states—and more than 51% in just one (New York). Even among the party base—voters committed enough to participate in relatively low-turnout primary elections—liberals are in the minority. Moreover, many self-identified liberals are unlikely to also consider themselves "progressives," the preferred term of the Sanders campaign but a label that is not widely used in contemporary American political rhetoric. When Sanders talks about progressivism, in other words, many Democrats either won't be inclined to take his side or won't even know what he's talking about, and his accusatory use of the word "moderate" seems to ignore the millions of Democratic voters who describe their own politics in precisely those terms.