U.S. Sen. Elizabeth Warren (D-Mass.) backed recent negative comments on bitcoin by Treasury Secretary Janet Yellen during an interview with CNBC’s “Squawk Box” on Tuesday.

Asked if she agreed with Yellen’s comments made last month that the cryptocurrency was a “speculative” asset, Warren did not give a direct answer, saying, “I think Janet’s a really smart woman.”

When pressed, she said, “‘Speculative in nature and going to end badly’ – I don’t think Janet left a lot of room for ambiguity.”

CNBC’s host also clarified that Yellen had actually said bitcoin could “end badly for some.”

See also: Bitcoin’s Rise Should Make Regulators Ask if the Fed’s Policies Have a Hand in It: WaPo

The topic of bitcoin was brought up as a potential problem for a new “wealth tax” – proposed by Warren and Sen. Bernie Sanders (I-Vt.) on Monday – that would see rich individuals charged 2% annually on their net worth above $50 million and 3% above $1 billion.

Yellen has been an outspoken critic of cryptocurrencies, calling them a “growing problem” and citing their use in illegal activity such as the drug trade and terrorist funding. However, she also said cryptocurrencies have the potential to “improve the efficiency of the financial system.”

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