A presidential bid that began almost a year ago with an embarrassing DNA test to prove her Native American roots has now become the dominant story of the Democratic race. Elizabeth Warren performed well in the debates, is rising in the polls, and on the stump has transformed herself from a professorial wonk into a hardscrabble Horatio Alger candidate with an affecting personal story: a young woman who rose from Norman, Oklahoma, to Harvard through affordable college now out of reach for much of the middle class.

While Warren still trails Joe Biden in nearly every national and state poll, the trend is striking—as is the looming gap between her considerable skills and Biden’s repeated stumbles. The strategic premises of her campaign are to claim the progressive mantle from Bernie Sanders, stake the “alternative to Biden” ground, and then engage in a one-on-one battle for the nomination.

There are significant challenges to this strategy, not the least of which is winning over a reasonable share of the African-American vote, where Biden dominates. In fact, the South Carolina primary in 2020 could be Iowa 2008, but in reverse. Back then, Barack Obama persuaded African-Americans that he was more than a symbolic candidate when he won the caucuses in an overwhelmingly white state. This time around, if Warren were to win a respectable slice of the black vote in South Carolina, she would prove to white liberals skeptical of her electability that she has support among a constituency without which no Democrat can win a nomination, or the presidency. […]