On October 22, the California Republican Party state convention voted to set up a procedure for the state party to endorse candidates in statewide primary elections, starting in 2018. See this story.
Many of the supporters of a top-two system hold themselves as being opposed to “party bosses” and “party control of elections.” The irony is that the top-two system in California has now caused both major parties to endorse candidates before the primary. At one time in California it was illegal for political parties to endorse candidates in their own primaries, although that law was struck down by the U.S. Supreme Court in 1989 in Eu v San Francisco County Democratic Central Committee. Still, even after parties gained the free speech right to endorse candidates in their own primaries, they did not begin to do so until the top-two system came into existence.
GEE- BACK TO THE VERY BAD OLDE DAYS BEFORE THE 1888-1890 *OFFICIAL* PRIMARIES —
HAVING THE HACK BOSS GANGSTERS TRYING TO CONTROL NOMINATIONS.
No primaries, caucuses and conventions.
PR and AppV
SB 6 explicitly provided for party endorsement to be carried in the sample ballot distributed to every voter prior to the election. The American Independent Party has regularly exercised this authority when they did not have a candidate on the ballot.
Any objection to the party bosses would be to their directly placing candidates on the ballot, or preventing candidates from running.
Before adoption of the Australian ballot, there was nothing to prevent multiple candidates running and claiming to be whatever party they wanted to.