Center-left think tank Third Way urgently called on the Democratic front-runners of the 2020 presidential election to challenge Sen. Bernie Sanders on the South Carolina debate stage on Feb. 25, in a memo provided to Axios' Mike Allen on Saturday.

What they're saying: "At the Las Vegas debate ... you declined to really challenge Senator Sanders. If you repeat this strategy at the South Carolina debate this week, you could hand the nomination to Sanders, likely dooming the Democratic Party — and the nation — to Trump and sweeping down-ballot Republican victories in November."

"We have seen this movie before. While there is no moral equivalence between Donald Trump and Bernie Sanders (none whatsoever), there is similarity between this moment and the 2016 Republican race. When Chris Christie took on Marco Rubio in their debate, it mortally wounded both candidacies and gave Trump a clear path to the nomination," Third Way co-founders Jon Cowan and Matt Bennett write.

The state of play: The memo — addressed to former Vice President Biden, former New York Mayor Mike Bloomberg, former Indiana Mayor Pete Buttigieg, Sen. Amy Klobuchar and Sen. Elizabeth Warren — comes as Sanders sweeps past other candidates in top national polls.

Full memo.

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