After an LAPD investigation, authorities issued a warrant for 30-year-old Scott Hounsell. He was booked on two misdemeanor counts of sending harmful matter to a child, police said. Hounsell is being held on $40,000 bail.
Jonathan Wilcox, a spokesman for the county's official Republican organization, said Hounsell resigned on June 15 for an unrelated reason.
"We take this issue very seriously and will fully cooperate with law enforcement any way we can," Wilcox said.
Wilcox said the organization didn't know about the case until contacted by the LAPD on Friday.
Hounsell worked previously as a field representative and internship coordinator for California state Assemblyman Cameron Smyth.
The Associated Press contributed to this report.