(CNN) There will be 10 Democratic presidential candidates onstage Thursday night in Houston, Texas. But all eyes will be -- and should be -- on only two: Joe Biden and Elizabeth Warren.

Biden and Warren are, and likely will continue to be, the yin and yang of the battle to be the Democratic standard-bearer in the 2020 election. Biden is establishment, incremental and pragmatic. Warren is outsider, swing-for-the-fences and idealistic. Biden has been the race's front-runner since the beginning. Warren is rapidly stealing the spotlight from Bernie Sanders within the party's progressive wing.

They represent, broadly, the two paths before Democratic voters, who will spend the coming months figuring out which option has the better chance of defeating President Donald Trump. And remarkably, they've never shared a debate stage before.

All of which means we -- and they -- will be in uncharted territory tonight. Which is exciting!

That said, both candidates have already provided very clear hints about what they view to be the other's major weakness, and a close reading of those comments tells us a lot about the ground on which Thursday's debate will be fought between its two most important players.

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