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 has 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, saidin 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 Obama, who 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 US 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.

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 longstanding 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 14.7 million voters.

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

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.