Story highlights Bernie Sanders has been poking at Hillary Clinton's past paid speeches to Goldman Sachs

"By the way, without naming any names, Goldman Sachs also provides very, very generous speaking fees to some unnamed candidates"

Carroll, Iowa (CNN) Bernie Sanders has a new bus for the last two weeks before the all-important caucuses in Iowa and also a new strategy: attacking Hillary Clinton where she's most vulnerable.

Sanders has been inching there for months now, but he finally dropped the nice-guy routine this week -- and with an only slightly coy hit on knitting together Clinton's fabled speaking fees and her Wall Street connections.

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"By the way, without naming any names, Goldman Sachs also provides very, very generous speaking fees to some unnamed candidates," Sanders said, as the crowd chuckled. "Very generous. Now I know that some of my opponents are very good speakers, very fine orators, very smart people, but you gotta be really really, really good to get $225,000 a speech. That's all I'll say."

He obviously did not need to name names; a member of the audience yelled, "It was $600,000!"

Sanders laughed and said, "That's for three speeches."

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