Trump called the fraud "serious" in the state, along with Virginia and New Hampshire, and blamed media "bias" for the lack of coverage the allegations have received.
It was the first time the president-elect has specifically voiced concerns about voting in California. The tweet came in the wake of several days of criticism from both Trump and his advisors over an effort by the Green Party to force a recount of votes cast in Wisconsin and possibly Michigan and Pennsylvania.
The tweet, posted on Sunday afternoon, was met with condemnation from the state's top elections official.
“It appears that Mr. Trump is troubled by the fact that a growing majority of Americans did not vote for him,” Secretary of State
Elections officials in the state’s 58 counties have not yet completed counting the ballots cast this month, but there’s no doubt Trump was trounced by Democrat
The president-elect's Sunday comments are not in line with any reporting or investigations into intentional acts in California designed to influence the outcome of the vote. Even so, the concern for voting integrity was echoed by a top state Republican.
"I just think our system is ripe for fraud in California," said Harmeet Dhillon, the former vice chair of the California Republican Party and current Republican National Committee member.
Dhillon said she had not seen evidence of a systemic effort to rig California's elections, but said Republicans had often raised concerns about election operations. In particular, she criticized the state's relatively new law that requires the counting of any absentee ballot postmarked by election day and arriving as long as three days late. She said it was possible a ballot envelope could be postmarked using a private postage meter that had been set to Nov. 8 but was cast the next day.
"The word 'postmarked' is not clear in the law," said Dhillon, a San Francisco attorney.
But any such incident would be too isolated to sway a statewide election such as the presidential contest. Trump's accusation, offered as so many of his tweets without any further explanation or substantiation, stood in contrast to what otherwise at this point are only a series of vignettes about ballot or election mistakes in California.
"Broad-brush allegations of voter fraud and illegal voting serve only to undermine the public's trust and confidence in the elections process and run the risk of further deflating voter participation," said Dean Logan, registrar of voters in Los Angeles County and president of the statewide association of elections officials.
Unlike other states, elections observers point out that California has a series of safeguards built into the systems used by individual counties and overseen by state officials. Those include voter-verified paper records for any ballots cast by electronic device (though the preponderance of votes are now cast using optical-scan ballots) and a 51-year-old law requiring an audit of the results in all races by hand-counting 1% of the ballots in each precinct across the state.
"California has the most robust voting verification laws of any state in the country," said Kim Alexander, president of the nonpartisan California Voter Foundation.
In the almost three weeks following Trump's election, numerous online posts have alleged — with no actual evidence — voter fraud in various places across the country, often tied to allegations that those votes came from immigrants in the U.S. illegally.
Even so, Dhillon said the integrity of elections in California and across the nation is a serious issue that Trump is trying to highlight.
"I think a single fraudulent ballot is a serious instance of fraud," she said.