(CNN) After signing an executive order that will place a moratorium on the death penalty in California, Democratic Gov. Gavin Newsom gave an emotional explanation of his decision Wednesday, saying he could not morally allow executions in the Golden State to go forward.

At a news conference in Sacramento on Wednesday, Newsom noted that there are 737 people on death row in California -- 25 of whom have exhausted their appeals -- meaning that the state is tasked with "executing more people than any state in modern American history; (lining) up human beings every single day for execution for two plus years."

"It's a very emotional place that I stand in," he said, noting that the subject was once "an abstract question" for him, but now he is "the backstop" for any execution that takes place in California. "And so I am expressing this is not from (a) paradigm of politics. It's not a situational conversation for me. This is about who I am as a human being. ... To me this is the right thing to do."

Newsom noted that the only thing standing in the way of executions resuming in California is the judicial review of the state's lethal injection procedure, which could be completed soon. Citing a National Academy of Sciences report estimating that 1 out of every 25 people on death row is innocent, Newsom said he could not countenance the odds of putting an innocent person to death.

"If that's the case, that means if we move forward executing 737 people in California, we will have executed roughly 30 people that are innocent," Newsom said. "I don't know about you. I can't sign my name to that. I can't be party to that. I won't be able to sleep at night."

Newsom said he made the decision "with a heavy heart" and "deep appreciation of the emotions that drive this issue" after meeting with more than a dozen family members of victims over the past few weeks.

"I met someone yesterday," he saidm recounting those conversations with families of victims, "who said, 'This is about eradicating evil and you have a responsibility to eradicate evil by executing those on death row.' I met a mother who said, 'How dare you. You have no right to do this to my family. You won't be doing this for my family. You'll be doing this to my family. You have no right to take another life in the name of my daughter who was murdered.' These are tough things to square. These are hard things to process. ... But we cannot advance the death penalty in an effort to try to soften the blow of what happened."

The policy will serve as an instant reprieve for the 737 people on death row in California, which has the largest death row population in the nation. The governor said the equipment in the execution chamber at San Quentin State Prison was already being dismantled, and that he was withdrawing California's lethal injection protocol. The order will not alter any current conviction or sentence, or lead to the release of any prisoner currently on death row.

With Newsom's move, California joins Colorado, Pennsylvania and Oregon as the fourth state to place a moratorium on the death penalty, though the length and reasoning for the moratoriums vary from state to state. The decision was derided by President Donald Trump Wednesday morning, who tweeted that Newsom was "defying voters" and that the "Friends and families of the always forgotten VICTIMS are not thrilled, and neither am I!"

Newsom's decision also drew criticism from several California lawmakers, who noted that California voters defeated ballot propositions in 2012 and 2016 that would have ended the death penalty in the state. Lawmakers are working on another ballot proposition to that effect that could go on California's ballot in 2020.

California state Sen. Jim Nielsen, a Republican from Tehama who served on the California Board of Prisons for nearly two decades, said Newsom "callously disregards the anguish of these families and rips them from any sense of justice, victimizing them all over again."

"This executive order is an affront to our system of justice," Nielsen said. "California voters have spoken loudly and clearly, as recently as 2016, that the death penalty serves as a legal and appropriate punishment for those who commit vicious, evil crimes."

California's executions were essentially halted in 2006 when a condemned inmate challenged the state's protocol for lethal injection, ensnaring California in legal challenges that continue today. But Newsom faced a deadline, because that legal process could soon come to an end.

Newsom has long opposed the death penalty, but has been wrestling with what action to take as governor.

Just last month, Newsom issued an executive order that allowed for new DNA testing of evidence in the high-profile case of death row inmate Kevin Cooper, who was sentenced in 1985 for the murders of four people and has exhausted his appeals. Cooper has long maintained his innocence, and former California Gov. Jerry Brown, another Democrat, agreed to some limited retesting of evidence in the case last year.

Since becoming governor, Newsom has been meeting with the families of victims, as well as law enforcement officials, while consulting with his legal team about what action to take.

Ultimately, Newsom decided the moratorium was in the best interest of the state, because he believes the death penalty "is inconsistent with our bedrock values and strikes at the very heart of what it means to be a Californian."

Marc Klaas, the father of murder victim Polly Klaas, expressed his dismay about Newsom's decision during an interview with HLN's Mike Galanos on "True Crime Live."

Klaas, whose 12-year-old daughter was abducted at knifepoint from her mother's home in California during a sleepover in 1993, said that when Newsom told him of the decision during a meeting in Sacramento: "I have to tell you, I died a little bit once I processed exactly what he was saying."

Richard Allen Davis, who was convicted in the kidnapping and murder of Polly Klaas in 1996, is one of the men on death row who could be spared the death penalty by Newsom's decision.

"He feels the way he feels," Klaas said of Newsom. "This is Trumpian in nature. This is somebody using an executive order, an imperial executive order based on a whim to turn around the law as it exists and the will of the people. It's absolutely outrageous."

Klaas added that Newsom told him about the moratorium while the two men were having a longer conversation about victims' rights that he thought was "going very well."

"But the manner in which he did this at the very end of that conversation, to lay this on me -- and I was the only guy in the room who had a real stake in the death penalty -- it was a little bit sadistic."

In his speech on Wednesday, the governor highlighted the racial disparities in sentencing -- noting that 6 in 10 prisoners on California's death row are people of color -- the cost of enforcing the death penalty and the number of innocent people who have been sentenced to death.

Since 1973, a total of 164 prisoners nationally -- including five from California -- have been freed after they were wrongfully convicted, according to "The Innocence List" maintained by The Death Penalty Information Center.

In 2016 while serving as lieutenant governor, Newsom endorsed a failed California ballot measure that would have repealed the death penalty -- an issue so controversial that then-Gov. Brown and then-Attorney General Kamala Harris did not take positions. Aides to Harris, now a Democratic US senator and 2020 presidential candidate, have said she felt that she had a duty to uphold the death penalty as attorney general, even though she personally opposed it. She also remained neutral on ballot measures as attorney general because she was responsible for writing the title and summary language for all propositions

At that time, Newsom said he understood that the issue "raises deeply felt passions on all sides" but he believed that Americans ultimately would look back on the death penalty "as an archaic mistake."