Eric H. Holder Jr. was the US attorney general from 2009 to 2015. The views expressed in this commentary are his own. View more opinion articles on CNN.

(CNN) As 10 Democratic contenders take the stage this Thursday night for the next presidential debate, the most important question they'll face is one the moderators probably won't ask.

Eric H. Holder Jr.

Their judgment, experience, and positions on key issues are all important for primary voters to consider—and of course defeating Donald Trump and ending his corrupt administration must remain a top priority. But with polls suggesting, at this early stage, that victory could potentially be within reach for virtually any candidate , when I tune in this Thursday, the most important question on my mind will be which Democrat is the most effective advocate not only for her or himself, but for the record, vision and values of the Democratic Party of today and years past.

In other words: which candidate deserves to be not just our nominee in 2020, but our leader for the next generation?

The most recent round of debates, in July, was filled with missed opportunities to answer this question. Many candidates spent too much time in the weeds, developing "gotcha" moments or straining to draw personal or policy distinctions—at once testing viewers' patience and missing the forest for the trees.

This is not to suggest that the many differences between candidates are insignificant. But voters don't tune in to prime-time debates to watch hours of wonkish hair-splitting. They—we—are hungry for someone to present an affirmative vision for America, post-Trump.

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