Rep. Alexandria Ocasio-Cortez (D-NY) mocked former Sen. Joe Lieberman’s position that the freshman congresswoman’s policies do not represent the “future” of the Democratic Party — the latest sign of brewing tensions between the party’s progressive and establishment members.

In a Thursday interview with the Fox Business Network, Lieberman, who retired in 2013 after serving nearly 25 years in the Senate, poured cold water on Ocasio-Cortez’s ability to prosecute her progressive agenda. “With all respect, I certainly hope she’s not the future and I don’t believe she is,” the Democrat-tuned-Independent told host Neil Cavuto.

“If you look at the majority of new Democrats in the house, they tend to be, I say, center-left, if they are not left-left,” he continued. “And that is because they had to be center-left to win some of those competitive swing districts that they took from Republicans. So that’s the hope.”

On the subject of Ocasio-Cortez’s proposed 70% marginal tax rate to fund her “Green New Deal” — an economic stimulus program designed to transition the U.S. from fossil fuels to 100 percent renewable energy within 10 years — Lieberman said a progressive tax system already exists in the U.S.

“If you … accumulate income in the country the big bump is still in the middle class” said Lieberman. “So you’ve got to be careful about raising taxes too high … a 70 percent tax on high-income people is really done for political reasons.”

Shortly after, Ocasio-Cortez quote-tweeted Lieberman’s remarks with: “New party, who dis?”

“Who dis?” is a slang phrase deployed to avoid unwanted interactions through text messages by pretending that the messenger’s number is not tied to a name in one’s contacts.

The latest zinger from Ocasio-Cortez comes as House Democrat leaders are expressing frustration with the freshman congresswoman’s repeated attacks on establishment lawmakers. Incumbent Democrats are perturbed by Ocasio-Cortez’s vow to help unseat moderate Democrats, who she, along with other progressive lawmakers and advocacy groups, see as roadblocks to enacting their far-left agenda, which in addition to the Green New Deal, including “Medicare for All,” the cancellation of all student debt, and the abolishment of ICE.

“I’m sure Ms. Cortez means well, but there’s almost an outstanding rule: Don’t attack your own people,” said Rep. Emanuel Cleaver (D-MO) told Politico. “We just don’t need sniping in our Democratic Caucus.”

Some Democrats, such as Rep. Yvette Clarke (D-NY), are pushing the 29-year-old to hold off on the attacks and try building bridges in her first term. “I think she needs to give herself an opportunity to know her colleagues and to give herself a sense of the chemistry of the body before passing judgment on anyone or anything,” Clarke said in an interview with Politico.