A Sanders campaign spokesman declined to comment to POLITICO.

O’Brien was drawing — sometimes inaccurately — from essays Sanders wrote in the 1960s and ’70s for the alternative newspaper The Vermont Freeman. The future senator once referenced studies purporting to link cervical cancer with sexual activity — but his concern was actually women having too few orgasms, not too many.

Sen. Bernie Sanders. | Joshua Lott/Getty Images

A 1972 essay included rape fantasies from both a man’s and a woman’s perspectives, though Sanders in 2015 disavowed it as “poorly written” fiction akin to “Fifty Shades of Grey.”

And a 1969 piece criticized restrictions on babies being naked at the beach. Sanders wrote, “Now, if children go around naked, they are liable to see each others sexual organs, and maybe even touch them. Terrible thing! If we [raise] children up like this it will probably ruin the whole pornography business.”

The Bloomberg campaign’s move to resurrect these comments comes as the fractured field of Democratic moderates is struggling to blunt Sanders’ momentum — and to convince primary voters ahead of a debate in South Carolina on Tuesday night that the Vermont senator is a bad bet for the general election.

Also on Tuesday, Bloomberg held a South Carolina press conference where black surrogates attacked Sanders’ record. Bloomberg has released two new online ads slamming Sanders for his past votes on guns and for his supporters’ online behavior. O’Brien, after invoking the old essays, pivoted to Sanders’ record on immigration, guns and the 1994 crime bill.

But the efforts to paint Sanders as too radical for November haven’t paid off yet: Recent POLITICO/Morning Consult polling found that Democratic primary voters now see him as the most electable primary candidate.

Christopher Cadelago contributed to this report.