There wasn’t one Democrat and one Republican on every congressional ballot but there was on the assembly ballot. There were roughly the same number of two party Presidential votes as there were assembly votes. The voter drop-off roughly corresponded with the third party Presidential vote. Trump lost 54.6%=45.4%, but Republican assembly candidates won 56.6%-43.4%. Trump got 492,152 votes. GOP assembly candidates got 615,755.
Darrell Issa clearly has a target on his back in every election from here on. The other three Republicans all managed to get at least 57% of the vote. There's no indication they'll be in trouble for at least the next two cycles. Redistricting will take place for the 2022 cycle. I have no idea how that'll impact the districts. Replace a Republican city or two from Ed Royce's district with Democratic ones and he'll lose too. Fortunately for Republicans the lines won't be drawn by Democrats but by an independent commission.