SALEM, Ore. >> A parade of Republican-controlled states in recent years has made it more difficult to cast a ballot, imposing strict identification requirements at polling stations, paring back early-voting periods and requiring proof of citizenship to register.

Then there is Oregon. It is leading what could become a march in the opposite direction.

From January through April, Oregon added nearly 52,000 new voters to its rolls by standing the usual voter-registration process on its head. Under a new law, most citizens no longer need to fill out and turn in a form to become a voter. Instead, everyone who visits a motor-vehicle bureau and meets the requirements is automatically enrolled. Choosing a political party — or opting out entirely — is a matter of checking off preferences on a postcard mailed later to registrants’ homes.

With the change, Oregon now boasts perhaps the nation’s most painless electoral process; mail-in ballots long ago did away with polling places’ snaking lines and balky voting machines

Whether painless equals effective, however, is another question. For while officials here hope automatic registration fuels a jump in voter turnout, the results of experiments elsewhere and the statistics from last month’s Oregon presidential primary — the first in which the new voters could cast ballots — have been decidedly mixed. Getting more people registered, it seems, does not necessarily mean getting more people to vote.

Regardless, Oregon’s example is gaining traction. California, Vermont, West Virginia and, this week, Illinois have followed Oregon in enacting automatic-registration laws; none have yet been put in effect. Twenty-three other states and the District of Columbia have considered similar measures since last year, according to the Brennan Center for Justice at New York University’s School of Law.

“I think states like Oregon, West Virginia and the others deserve a lot of credit for trying to bring voting rights into the 21st century,” said David Becker, director of election initiatives for the Pew Charitable Trusts.

Yet in a year when voting is as much a partisan football as a patriotic duty, even the civics book notion of expanding the electoral franchise has a political cast. To many conservatives, automatic registration is largely a Democratic pushback to a wave of voting restrictions enacted by Republican state legislators who claim to be combating voter fraud. Most experts say the kind of fraud the laws are said to target barely exists.

Just as Republicans may assume — and sometimes say outright — that voting restrictions depress Election Day turnout of students, minorities and other traditionally Democratic constituencies, Democrats may assume that expanding registration will bring more of those same voters into their fold.

“When you get people living in poverty, people of color, young people registered, yes, they tend to vote progressively,” Jennifer Williamson, the Democratic majority leader of the Oregon House of Representatives, said in an interview. “But regardless of what the outcome is, removing the barriers for people to vote is the right thing to do.”

Excepting West Virginia, the states that have enacted auto-registration laws are controlled by Democrats. A Chicago-based group mounting a nationwide campaign for the laws is headed by former political strategists for President Barack Obama, who also has urged the states to follow Oregon’s lead.

Oregon’s bill became law without a single Republican vote. So did California’s. And while Vermont and West Virginia registration laws won bipartisan backing, some analysts suggest that was partly because those states have too few unregistered minorities to be points of political dispute.

If automatic registration gains steam nationally, however, the impact could be sizable.

The U.S. Census Bureau says that at least 41.1 million of the 219 million people eligible to vote in 2014 were not registered. California alone had roughly 6.6 million eligible but unregistered voters as of October, state officials said.

Enrolling them could conceivably change the political landscape. While the majority are white, census data show they are also disproportionately Asian and Hispanic, lower-income and young. Other studies indicate they are less educated and less engaged with politics and their communities than are regular voters.

While those characteristics often fit Democratic voters, that is not always so. Lower-income, less-educated white voters, for example, are reliably Republican and are strong supporters of Donald Trump’s presidential bid.

Whatever their leanings, the crucial question is whether they will turn out on Election Day. The answer is unclear.

Samuel Wang, a Princeton University professor of neuroscience and a long-standing elections analyst, leads the optimists. He notes that participation in programs like organ donation and savings plans rises dramatically when people have to opt out of them instead of opting in.

In jurisdictions that allow Election Day registration at polling stations — a method almost as simple as automatic registration — average turnout is 7.8 percentage points above the national average, he said. Were automatic voter registration to generate the same increase, the electorate would gain 14.7million voters.

“It will potentially have a larger increase than any amount of shoe-leather get-out-the-vote,” he wrote in an email.

But many experts are skeptical. The citizens swept onto the rolls by automatic registration, they say, are by definition those who have not made voting a priority. And the political landscape is littered with electoral fillips that had little impact on Americans’ sorry electoral behavior.

“Most studies show that election reforms don’t affect turnout very much, and when they do, the people who turn out look a lot like the people who are already voting,” said Barry C. Burden, director of the University of Wisconsin-Madison’s Elections Research Center.

The 1993 National Voter Registration Act — the “motor voter” law — aimed to increase registration by requiring motor vehicle and public-assistance offices to offer patrons a chance to enroll as voters. But one study concluded that motor-vehicle bureau registrations have remained fairly constant, even as the population has increased.

Voting by mail vastly simplifies casting a ballot, and the states that mandate it — Oregon, Colorado and Washington — have turnout rates well above the national norm.

Yet states from Mississippi to Minnesota have comparable or even higher turnout. And studies in California and Washington suggested that mail-in ballots generally raise turnout only when combined with other get-out-the-vote efforts.

Delaware’s electronic registration system is all but automatic: computers flag unregistered motor-vehicle bureau customers, and clerks offer them a paperless registration process that requires only a signature on an electronic pad.

The state’s elections commissioner, Elaine Manlove, raves about it. “We have no paper anymore,” she said. “It freed up tons of office space and made things faster.”

But from 2010 to 2015, state records indicate, Delaware added only about 26,000 Democrats and independents — and lost 2,853 Republicans. That’s an increase of less than 4 percent.

And Oregon? Secretary of State Jeanne P. Atkins says the jury is still out.

By one measure, citizens greeted auto-registration with a yawn. Of the 55,092 Oregonians automatically enrolled at motor-vehicle offices through April 30, only 12,621 mailed back postcards regarding their registration status — and about one in three asked to be deregistered.

Of those who chose a party, 4,776 ticked the Democratic checkbox, a share considerably greater than the party’s 41 percent share statewide. Another 2,671 became Republicans, well below the party’s 28 percent share.

Jim Moore, a political-science professor and election analyst at Oregon’s Pacific University, said election reforms like mail-in balloting have triggered similar bumps in Democratic registration or turnout, but they were short-lived. “In the long run, everything settles into its demographic place and the electorate reflects who we are as a people,” he said. “This doesn’t say anything about the next election.”

The good news was that those voters turned out in droves to support their presidential candidates, in proportions roughly equal to Democratic and Republican turnout statewide. But unaffiliated voters — those who never returned a postcard — all but stayed home. Although unaffiliated voters could not vote in the presidential primaries, more than 1 in 5 statewide still cast ballots in nonpartisan races. Among those who were automatically registered, however, the number was closer to 1 in 16.

Atkins, the secretary of state, said any genuine impact of the registration changes will be clear only after more voters are automatically enrolled and can vote in elections open to everyone. The voters enrolled through April comprise less than 2 percent of the state’s registered voters. “We have a lot to learn over the next several election cycles,” she said, “but I think we can say so far, so good.”