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Elizabeth Warren has been quietly chipping away at her progressive pal Bernie Sanders for weeks.

On Tuesday night, she upped the ante during her opening comments. Warren said she was on Sanders' side on a number of issues, but then attacked the front-runner over his approach to health care.

"Bernie and I both want to see universal health care, but Bernie’s plan doesn’t explain how to get there. Doesn’t show how we’re going to get enough allies into it and doesn’t show enough about how we’re gonna pay for it," Warren said.

And then, the dagger:

"I dug in, I did the work (on the financing) and then Bernie’s team trashed me for it," Warren said.

Warren was subject to some progressive criticism after she released her Medicare for All financing and transition plans. Sanders and his campaign offered some mild criticism. His supporters, though, were more aggressive, questioning Warren's commitment to the legislation.