BLUE ON BLUE: Conflicting Interests Split Top Democratic Firm.

A top Democratic consulting firm, Mack|Crounse Group, split this month after one of the partners used a shell firm to produce mail pieces that attacked candidates backed by the other partner’s banner progressive clients.

The break-up between longtime partners Kevin Mack and Jim Crounse illustrates how the complications of modern politics — outside spending, jungle primaries and interest groups — can put a firm in conflict with itself.

For five cycles, Mack|Crounse Group was a giant among Democratic mail firms, counting top liberal groups, labor unions, elected officials and even President Barack Obama as clients. But all it took to fell the famed partnership were two obscure state California Assembly races last fall.

“Colossal mistakes were made on the other side of a firewall,” Mack said in a phone interview Wednesday. “I was blindsided by this a month or so ago. Those mistakes left me no choice but to split the firm.”

Oops.