Jerry Brown, the former governor, left office recently with a $15 million campaign war chest, and has said some of that money can be used to defend his criminal justice legacy by trying to defeat the ballot measures.

The data on crime, and what it says about reforms, has been contested. Small upticks in some types of crime in some areas has muddied the picture. And Californians may well be confused about what to believe: One day, headlines say that crime is up; the next, that crime is down. For instance, violent crime rose in California in 2012 and between 2015 and 2017, allowing opponents of the laws to point to increases, even as scholars say arguments about criminal justice policies should not be based on short-term fluctuations — and that overall crime rates are declining.

Activists see parallels in the strategies of opponents of more lenient sentencing laws in California and the rhetoric on crime at the national level. The former attorney general, Jeff Sessions, warned early last year about a “staggering increase in homicides.” Violent crime had ticked up in 2015 and 2016 after a long decline, but when F.B.I. statistics for 2017 were released — after Mr. Sessions’s warning — they showed that violent crime had gone down again.

One of the most controversial changes in California was a law passed last year to end cash bail. Initially anticipated by liberal activists as a significant step to end the practice of holding poor defendants in pretrial detention because they could not afford bail, the final version of the law has been disavowed by many of its early supporters. That is because, activists say, the law gives judges more discretion to hold the accused before trial. The new system will also use algorithms to assess whether a defendant is a flight risk or might commit another crime — tools that activists say are biased against people of color.

“It gives judges basically unlimited power without due process,” said John Raphling, a senior researcher at Human Rights Watch in Los Angeles. The risk assessment tools that judges would use, he said, “embed racial bias.”

The controversy over the bail law has essentially placed the bail industry and civil liberties advocates like the A.C.L.U. on the same side. But it is the bail industry that has backed a ballot measure to overturn the law, which has received enough signatures to go before California voters in 2020.

In pushing the measure, the industry has offered contradictory arguments, sometimes suggesting that eliminating cash bail would mean more criminals on the streets, and other times adopting the argument of the liberal activists that the new law could, in fact, end up locking up more people in a manner that would be unfair to poor African-Americans.