Bouie's main conclusion, with which I concur unreservedly, is that committed liberals remain a minority within the Democratic Party. "The broad point," he writes, "is that a 'political revolution' can’t rest on a call for clean government and ideological rigor—the crux of Sanders’ general argument. The Democratic Party isn’t yet an ideological party, and many of its voters don’t put ideology or good-government reform at the top of their lists." From the standpoint of accumulating delegates, Sanders's fate was sealed by his inability to convince a greater share of African-Americans and other racial minorities that he would better represent their views and interests than would Hillary Clinton. The Democratic Party is a group coalition, and Sanders was unable to build a broad enough alliance of groups within the party to overtake Clinton in the national delegate count.
The pattern of a liberal insurgent losing a Democratic nomination race to a more moderate, transactional rival is a common one; Sanders's counterparts in previous years include Howard Dean (2004), Bill Bradley (2000), and Jerry Brown (1992). Because Sanders outperformed these predecessors, Bouie suggests that his campaign could serve as the foundation for the rise of a new liberal movement that might succeed down the road in capturing control of the Democratic Party, just as the modern conservative movement identified with Barry Goldwater and Ronald Reagan became the dominant faction of the Republican Party by the 1980s. In my view, however, this remains an unlikely development. Among the reasons why:
1. It's unclear how much of Sanders's electoral success is a product of Hillary Clinton's specific weaknesses. In particular, his overwhelming margins among young voters might have been attenuated had he been facing a more conventional Democratic opponent, or opponents, who could also claim to be a fresh political face and who remained free of the baggage left by the Clintonist compromises of the 1990s and early 2000s. If Sanders were running against some combination of Cory Booker, Chris Murphy, and Amy Klobuchar, would voters under the age of 35 appear equally enthusiastic about the prospect of implementing socialism as the defining creed of the Democratic Party?
2. Because Sanders is not himself a Democrat, he is not in a position after the election to lead an internal faction of Democratic politicians and activists dedicated to remaking the party as a vehicle of the liberal cause—and it is unclear who else within the party has the national standing and influence to do so on his behalf. Elizabeth Warren is the most likely figure, although it is unclear whether she wishes to play such a role. Sanders disproportionately receives support from voters who are not themselves Democratic identifiers; why would we expect these voters not only to join the Democratic Party but also to become active within its ranks if their political hero has never done the same?
3. The American left, such as it is, has long had an ambivalent relationship with electoral politics in general and Democratic Party politics in particular. While the conservative movement threw itself into gaining root-and-branch control of the Republican organizational apparatus and using it to persuade and mobilize voters on behalf of conservative candidates, there has been no sustained counterpart to these efforts on the left; leftists often prefer other forms of protest such as marches, occupations, boycotts, and internet activism. (To take a recent example, compare the Tea Party movement to the Occupy movement. One side emphasized engagement in partisan politics and electoral participation on behalf of a policy agenda, the other did not. Which approach was more successful?) The current activity on behalf of the Sanders campaign will not be sustained past the end of his candidacy if his supporters view his defeat as signaling the futility of electoral mobilization rather than as a promising start upon which to build a sustainable movement.
4. The final triumph of the conservative movement within the Republican Party did not occur until Ronald Reagan demonstrated that a conservative candidate could win a national election, thus removing the strongest remaining justification for the existence of moderate Republicanism. It is unclear at best whether a Sanders-style liberal is electable; Bouie notes that left-wing Democrats are rarely elected statewide even at the sub-presidential level outside of the Northeast and coastal West.
Even if a future Sandersesque candidate manages to win the Democratic nomination, a general-election defeat would only reinforce the instincts of many party actors that purist liberalism is, regardless of its other merits, ballot-box poison in the United States. As a result, non-purist Democrats would gain substantial justification for their efforts to swing the party back toward the center (as previously occurred in the mid-1970s and early 1990s).
5. Finally, it is unclear whether Sanders-style liberalism would be successful as a governing strategy even if granted officeholding power by the American electorate. Sanders is less interested than most Democrats in conceding ground to expert-dominated technocracy or the constraints of political pragmatism, which allows him to propose a bold legislative agenda and make campaign promises that remain appealingly unrestrained by the disappointing limitations of practicality. Once the election is over, however, the concrete demands of Democratic constituencies will not be satisfied by mere symbolic measures. Sanders's single-payer health care plan, for example, may be more ideologically pure than Obama's comparatively kludgy Affordable Care Act, but if he can't get it passed—or if it is enacted but fails to provide the benefits that it promises—than many Democratic supporters will judge his approach wanting, and look around for an alternative strategy that doesn't make the perfect the enemy of the good.
The current "impure" nature of the Democratic Party does not reflect the triumph of corrupt corporate sellouts over innocent idealists, but instead represents the hard-won experience of most core groups within the party coalition that incrementalism and ideological flexibility are the best way to realize their political goals. If Sanders, or a future Sanders type, wishes to convince Democrats to dispense with that assumption, he or she would need to demonstrate that a more dogged adherence to ideological doctrine is equally if not more successful in addressing the specific social problems that Democratic constituencies seek to solve. Until then, the Democratic Party will remain a party on the left, but not truly of the left.