Here are the facts around Trump's recent claims on voting by mail.

The President has focused some of his ire on California Gov. Gavin Newsom's recent executive order to send mail-in ballots to all registered state voters for the November elections. When asked about the order on Thursday, Trump lashed out, claiming this policy of state-wide, mail-in voting has "tremendous potential for fraud and abuse." He further insinuated that Democrats won seven congressional elections by having individuals steal and forge signatures on mail-in ballots. "We had seven elections for Congress and they were like tied and they lost every one of them because they came and they dropped a whole pile of ballots on the table. But you don't think they rip them out of mailboxes?" Trump said.

The President also claimed that "kids go and they raid the mailboxes and they hand them to people that are signing the ballots down the end of the street, which is happening, they grab the ballots. You don't think that happens? There's ballot harvesting."

Facts First: While Trump's quote is confusing, there is no evidence to back up his claims about widespread ballot theft or signature forgery across California. Furthermore, there's no evidence ballots counted on or after election day in California's 2018 elections were illegally obtained or "harvested."

It's possible Trump is referring to 2018 when Democrats won seven seats in Orange County, California, receiving a boost from votes tabulated after election day, predominantly from absentee and provisional ballots, the Associated Press reported.

In 2016, California passed a law that allowed non-family members to submit other people's vote-by-mail ballots, which is referred to by some as "ballot harvesting." Prior to this, only family members or those in the same household could submit those ballots.

Despite allowing so-called ballot harvesting, California still has processes in place to verify that the signature on a ballot matches that of the registered voter the ballot belongs to. The situation of ballot theft and forgery Trump describes remains illegal and is highly unlikely to occur in US elections.

At the time, California's secretary of state told the AP that the reason votes in 2018 took weeks to tabulate was to confirm that every vote among the 20 million registered voters was counted correctly.

In Tuesday's tweets, Trump claimed that if states institute mail-in voting, then "ballots will be forged & even illegally printed out & fraudulently signed."

Most ballot envelopes have a bar code that election officials and/or the US Postal Service can track. These bar codes both allow voters to check that their ballots have been received and states to easily eliminate any duplicate ballots because a unique code is assigned to each voter. For voters able to leave their homes, many states, like Colorado, also have secure drop-off locations and drop boxes to reduce any theft or tampering of the ballots they received by mail.

It's unclear what Trump was referring to when he suggested that mail-in ballots would be "illegally printed." Ballots sent by mail are designed by the states, then the envelopes are approved by the USPS and everything is printed by a certified vendor.

To avoid ballots that are "fraudulently signed," about a third of states verify signatures and match voter information from ballots to existing voter registration records. While this practice has been criticized for potentially disenfranchising certain populations from voting, when handled properly using third-party software, a bipartisan review and individual outreach to voters whose ballots are flagged, it has been shown to effectively prevent voter fraud, especially on a large scale.

Trump tweeted that "there is NO WAY (ZERO!) that Mail-In Ballots will be anything less than substantially fraudulent."

Facts First: While rare instances of voter fraud from mail-in ballots do occur, it is nowhere near a widespread problem in the US election system.

In both 2016 and 2018, approximately 25% of US voters cast mail ballots, which includes the handful of states that conduct elections entirely by mail and traditional absentee ballots.

Justin Levitt, a professor at the Loyola Law School, Los Angeles, reviewed US elections from 2000 to 2014 and found 31 incidents of voter fraud from that time, during which more than a billion votes were cast.

A recent article from the Brennan Center for Justice, a nonpartisan, liberal-leaning think tank, also notes that "none of the five states that hold their elections primarily by mail has had any voter fraud scandals since making that change." Earlier in his administration, Trump's own voter fraud commission disbanded without releasing any evidence to back the President's claims of rampant voter fraud in the US.

Richard Hasen, a professor of law and political science at UC Irvine, told CNN that while "absentee ballot fraud happens at relatively higher rates than other kinds of election fraud," that overall rate is still "quite low."

"From my study of this over 25 years ... I don't see the amount of fraud as large at all," Hasen said. "But when fraud does happen, it tends to be caught."

One of the most notable recent examples of alleged fraud took place in 2018, when absentee ballots allegedly were illegally picked up and falsified in a North Carolina congressional race under the direction of a political operative who was working on behalf of the race's Republican candidate. That operative, Leslie McCrae Dowless, now faces obstruction of justice and perjury charges.

But experts argue mail-in voting is secure. "The bottom line is that absentee and mail balloting are secure in America," Wendy Weiser, the director of the Democracy Program at the Brennan Center, told CNN. "Election officials, Republicans and Democrats alike, pretty much universally are confident in the system."

According to a Fox News poll conducted in May, 63% of respondents support allowing all US citizens to vote by mail in the 2020 presidential election because of coronavirus. Trump himself has voted by mail in several elections and as recently as Florida's primary in March.

In his tweet the President also said that California Gov. Gavin Newsom "is sending Ballots to millions of people, anyone living in the state, no matter who they are or how they got there, will get one."

Later on Tuesday Trump repeated his claim during a news conference, saying that "people that aren't citizens, illegals, anybody that walks in California is gonna get a ballot."

Facts First: This is completely false. Newsom's order provides mail-in ballots only to people who are registered to vote. Noncitizens, including undocumented immigrants, are explicitly not permitted to register to vote in federal elections.

There have been some news reports that errors by government employees may have allowed small numbers of noncitizens to register to vote in California and in some other states. Regardless, Trump's claim that Newsom is sending a ballot to every single noncitizen remains false.

Trump's comments on Tuesday came after the Republican National Committee and other Republican groups filed a lawsuit against California to stop it from mailing absentee ballots to all voters ahead of the November election.

Although support for mail-in voting remains largely divided on partisan lines, Democratic and Republican state officials routinely oversee elections where millions of people vote by mail without systematic problems.