Lately, a rough consensus has emerged among people who study the impact of voting policies: Though they often spark fierce partisan fighting, most changes to voting laws do little to affect overall turnout, much less election results.

But one fast-growing reform appears to stand out as an exception.

When every registered voter gets sent a ballot in the mail — a system known as universal vote-by-mail — voting rates tend to rise, numerous studies have found.

Advocates for mail voting say these findings haven’t gotten the attention they deserve, and that they should lead more states that want to boost turnout to adopt the practice.

“(T)o a remarkable degree, most of the nation’s leading journalists, democracy reform organizations and elected officials continue to largely ignore, downplay — or even dismiss outright — the potentially profound implications of these noticeably high turnout rates,” said a research paper released last month by the National Vote at Home Institute, which advocates for increased use of mail voting.

Currently, eight states — California, Colorado, Hawaii, Nevada, Oregon, Utah, Vermont and Washington — use universal vote-by-mail.

Vote by mail attacked by Trump

Efforts in recent years by many states to make it easier to vote by mail prompted a furious backlash from former President Donald Trump and his backers, who have repeatedly claimed, without evidence, that mail voting is dangerously vulnerable to fraud.

Perhaps no state incurred Trump’s wrath more than Nevada, which, along with California, introduced universal vote-by-mail in 2020 in response to the pandemic.

“The governor of Nevada should not be in charge of ballots. The ballots are going to be a disaster for our country,” Trump said ahead of the 2020 election, referring to the state’s then-governor, Democrat Steve Sisolak.

In fact, Sisolak was not “in charge of ballots.” Secretary of State Barbara Cegavske, a Republican, was. “You’re going to have problems with the ballots like nobody has ever seen before,” Trump said.

Since replacing Sisolak this year, Gov. Joe Lombardo, a Republican, has pushed for eliminating universal vote-by-mail. “Sending ballots to more than 1.9 million registered voters is inefficient and unnecessary,” Lombardo said in January.

But Democrats, who control the state Legislature, have shown no interest in scrapping the system.

So great was the GOP’s suspicion of the practice in 2022 that some voters were told by party activists to hold onto mail ballots and hand them in on Election Day at their polling place, rather than mailing them.

But Trump and Republicans have lately backtracked, telling supporters to take advantage of mail voting rather than handing an advantage to Democrats. In June, the Republican National Committee announced a new get-out-the-vote drive encouraging early and mail voting.

States tinker with mail voting

Still, over 20 states have sought to restrict mail voting since 2020. Ohio has shortened the time frame to apply for mail ballots and imposed new signature requirements, while Arizona now removes people from its list to receive a mail ballot if they go for more than two years without voting.

Among states looking to expand mail voting, not all have gone as far as universal vote-by-mail. Both New York and Pennsylvania, among other states, have loosened their rules to allow anyone to cast an absentee ballot by mail, rather than requiring an excuse — a system known as no-excuse absentee. But the voter still must take the trouble to apply to receive their absentee ballot, rather than being mailed one automatically.

Experts say there isn’t strong evidence that these more modest approaches to mail voting do much to boost turnout. Other reforms that likewise have become core to the Democratic platform on voting policy, like adding early voting opportunities, also haven’t consistently been shown to increase voting rates. Allowing people to register at the polls — often called same-day registration — has in some studies been associated with small turnout increases.

By contrast, the research on universal vote-by-mail finds a consistent and significant impact.

Advocates say that’s hardly surprising. Under universal vote-by-mail, election officials simply mail ballots to directly everyone on the voter rolls, almost literally putting a ballot in voters’ hands. Voters can return their ballot either through the mail or by leaving it in a secure ballot dropbox.