BLUE ON BLUE: Clinton attacks on Sanders make Dems nervous.

Hillary Clinton’s White House campaign is going negative against her left-wing rival Bernie Sanders — and a lot of unaligned Democrats think that’s a bad idea.

Her husband, former President Clinton, is leading the charge, hitting Sanders supporters as sexist on Sunday while accusing the Vermont senator of muddying facts.

The attacks come as Hillary Clinton faces a defeat — perhaps a heavy one — in the New Hampshire primary on Tuesday, according to opinion polls.

Clinton barely defeated Sanders in last week’s Iowa caucuses, and Monday brought rumblings of a possible staff shake-up.

The shift by the Clinton team to a more aggressive footing evoked memories for some of her 2008 campaign against Barack Obama, when Bill Clinton and other surrogates mounted attacks that were widely seen as counter-productive.

Clinton supporters worry that history might be repeating itself, and that the former president’s attacks could boomerang on his wife by turning off large swathes of the Democratic electorate.

“I know what’s happening: He is just pissed off,” said Democratic strategist Brad Bannon. “He hears the attacks. He saw how close things were in Iowa and he thinks they’re 20 points or whatever down in New Hampshire, so he blows up.

“When he speaks reasonably and in the true Clinton style, he is very effective,” Bannon added. “But when he goes crazy because he’s pissed off about the thing, that hurts her.”

Bill Clinton’s aggressiveness, those in the orbit of the Clintons say, is rooted in at least two factors.

First of all, the former president has believed for some time that the campaign has not been vigorous enough in countering Sanders’s populist rhetoric.

Secondly, Bill Clinton was conspicuously unhappy with the Iowa result, allies maintain — despite the campaign’s desire to put a brave face on the outcome and Hillary Clinton’s remark on caucus night that she was breathing a sigh of relief.

One ally said Bill Clinton was “peeved”; another, more colorfully, described his mood as “rip shit.”

Or something that rhymes with that.