Early this month, San Diego Unified Trustee Scott Barnet surprised the public with a midnight Facebook post announcing he wouldn’t run for re-election.

Now, just a few months before the June primary, Barnett appears bent on taking school board president Kevin Beiser along with him.

Barnett called me up this week to give me a better idea of why he was endorsing Amy Redding, who’s challenging Beiser. He sang Redding’s virtues – she’s smart, focused and would put kids first, he said.

But then, Barnett torched his colleague – for 40 minutes straight. He said that over the course of Beiser’s tenure he’s been too busy promoting himself to help other school board members reshape San Diego Unified.

Here are some pieces of shrapnel from that conversation:

• “This guy goes to more parades and ribbon-cutting ceremonies than any other politician I’ve ever met. He’s more interested in improving his image than he is in helping us make the tough decisions that improve the district.”

• “Time and time again we’ve been abandoned by a school board member who’s gone off to get himself nominated for an award.”

• “I’ve seen him run out in the hallway in the middle of a meeting to pacify the labor union and tell them he’s on their side.”

• “In his heart, he truly cares about children. But without exception he almost never acts on it. I saw this in him as a candidate — but I thought it would die down when he became a trustee.”

Barnett’s penchant for going rogue and throwing bombs has been well documented. But his sustained attack on a colleague is bold even for him.

Barnett bases part of his criticism on Beiser’s voting record. In February, Beiser told LGBT weekly that he’s tirelessly advocated for preserving music and visual arts programs in schools. He’s even won an award for his commitment to the arts.

Barnett says that Beiser’s votes contradict his image. He points to a vote in 2013 in which Beiser voted against a policy that Barnett says could have saved art and music teachers.

The two politicians have often found themselves on opposite sides of votes, but they’ve never been as openly critical of each other.

Barnett was speaking in the context of why he’s decided to back Redding against Beiser in the coming primaries.

Redding, who works as a parent-volunteer full time, has a long track record serving on district oversight committees and pushing for greater transparency on how the district spends its money.

When I reached Beiser, he said he knew Barnett endorsed Redding, but seemed surprised at the accusations his colleague leveled.

Beiser said his voting record clearly represents that children are his primary motivation, and that the decisions he’s made in his board tenure helped the district close the achievement gap and earn national recognition as a Broad Prize finalist.

“Those results I think speak volumes for the work I’ve done as a school board member,” Beiser said.

Beiser has a lengthy list of endorsements even without Barnett’s blessing, from the teacher’s union to the California Charter Schools Association.

Barnett said the endorsements point to the time Beiser has spent vote-seeking instead of helping other school board members carry the burden.

“Look, we’re politicians,” said Barnett. “We’re insecure narcissists — we all have that to a certain degree. But Beiser rises to a new level.”