Senator Bernie Sanders (D-VT) has been surging in recent polls and it is setting up a showdown with Senator Elizabeth Warren (D-MA). Politico writes that it’s due in part to endorsements Sanders received from progressive leaders and organizations:

Two groups run by young people — the Sunrise Movement, which seeks to combat climate change, and Dream Defenders, which advocates for people of color — endorsed him last week. He’s also won the backing of People’s Action and the Center for Popular Democracy, which together claim more than 1.5 million members, as well as three lawmakers in the so-called “Squad” and liberal-minded labor unions.

Sanders recently took the lead in a key poll from Des Moines Register, CNN and Mediacom, with 20% of potential caucus voters in Iowa. In the midst of this, there is news that Sanders’ campaign has been targeting Warren. Politico reports Sanders’ campaign workers have been using negative talking points about Warren.

The script instructs Sanders volunteers to tell voters leaning toward the Massachusetts senator that the “people who support her are highly-educated, more affluent people who are going to show up and vote Democratic no matter what” and that “she’s bringing no new bases into the Democratic Party.”

“I like Elizabeth Warren. [optional]” the script begins. “In fact, she’s my second choice. But here’s my concern about her.” It then pivots to the criticisms of Warren.

When asked about this new directive to go after Warren, Sanders seemed surprised.

Regardless of what Sanders is saying, the damage seems done. In responding to the attacks, Warren said, “We cannot nominate someone who takes big chunks of the Democratic coalition for granted. We need someone who will bring our party together.”

Expect some of this tension between candidates to boil over tomorrow at the latest Democratic debate in Iowa.