In 1992, both California Senate seats were contested. One was because of the normal election cycle; the other because the seat was vacated. How was it decided which candidates were running for which seat?
They determined it themselves when they filed their candidacy papers with the Secretary of State.
The more in depth answer answers the question, how did the parties decide who they preferred to have run for the short-termed seat? In this case, if memory serves me correctly, DiFei was asked to run for the two-year seat on the theory she had the better chance of managing to raise enough cash to win two senatorial elections in the course of two years. The gamble paid off.
That’s correct. Feinstein had the $$$$$ to run an election in 1992 against Wilson’s apointee (John Seymour, who was a sacrificial lamb and got whipped in the election) and again in 1994. That proved to be prescient on the part of the Democrats because the Republicans trotted out Michael Huffington (Cough! Gag!) in 1994 and he almost won. Feinstein had enough money, recognition, and at least the semblance of intelligence to hold off Huffington.
Feinstein isn’t receiving a very tough challenge in 2000 by the Republicans. Feinstein doesn’t really raise the money as much as just spend her husband’s sizeable fortune.