America’s next president could be eased into office not just by TV ads or speeches, but by Google’s secret decisions, and no one—except for me and perhaps a few other obscure researchers—would know how this was accomplished.

Research I have been directing in recent years suggests that Google, Inc., has amassed far more power to control elections—indeed, to control a wide variety of opinions and beliefs—than any company in history has ever had. Google’s search algorithm can easily shift the voting preferences of undecided voters by 20 percent or more—up to 80 percent in some demographic groups—with virtually no one knowing they are being manipulated, according to experiments I conducted recently with Ronald E. Robertson.

Given that many elections are won by small margins, this gives Google the power, right now, to flip upwards of 25 percent of the national elections worldwide. In the United States, half of our presidential elections have been won by margins under 7.6 percent, and the 2012 election was won by a margin of only 3.9 percent—well within Google’s control.

There are at least three very real scenarios whereby Google—perhaps even without its leaders’ knowledge—could shape or even decide the election next year. Whether or not Google executives see it this way, the employees who constantly adjust the search giant’s algorithms are manipulating people every minute of every day. The adjustments they make increasingly influence our thinking—including, it turns out, our voting preferences.

What we call in our research the Search Engine Manipulation Effect (SEME) turns out to be one of the largest behavioral effects ever discovered. Our comprehensive new study, just published in the Proceedings of the National Academy of Sciences (PNAS), includes the results of five experiments we conducted with more than 4,500 participants in two countries. Because SEME is virtually invisible as a form of social influence, because the effect is so large and because there are currently no specific regulations anywhere in the world that would prevent Google from using and abusing this technique, we believe SEME is a serious threat to the democratic system of government.

According to Google Trends, at this writing Donald Trump is currently trouncing all other candidates in search activity in 47 of 50 states. Could this activity push him higher in search rankings, and could higher rankings in turn bring him more support? Most definitely—depending, that is, on how Google employees choose to adjust numeric weightings in the search algorithm. Google acknowledges adjusting the algorithm 600 times a year, but the process is secret, so what effect Mr. Trump’s success will have on how he shows up in Google searches is presumably out of his hands.

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Our new research leaves little doubt about whether Google has the ability to control voters. In laboratory and online experiments conducted in the United States, we were able to boost the proportion of people who favored any candidate by between 37 and 63 percent after just one search session. The impact of viewing biased rankings repeatedly over a period of weeks or months would undoubtedly be larger.

In our basic experiment, participants were randomly assigned to one of three groups in which search rankings favored either Candidate A, Candidate B or neither candidate. Participants were given brief descriptions of each candidate and then asked how much they liked and trusted each candidate and whom they would vote for. Then they were allowed up to 15 minutes to conduct online research on the candidates using a Google-like search engine we created called Kadoodle.

Each group had access to the same 30 search results—all real search results linking to real web pages from a past election. Only the ordering of the results differed in the three groups. People could click freely on any result or shift between any of five different results pages, just as one can on Google’s search engine.

When our participants were done searching, we asked them those questions again, and, voilà: On all measures, opinions shifted in the direction of the candidate who was favored in the rankings. Trust, liking and voting preferences all shifted predictably.

More alarmingly, we also demonstrated this shift with real voters during an actual electoral campaign—in an experiment conducted with more than 2,000 eligible, undecided voters throughout India during the 2014 Lok Sabha election there—the largest democratic election in history, with more than 800 million eligible voters and 480 million votes ultimately cast. Even here, with real voters who were highly familiar with the candidates and who were being bombarded with campaign rhetoric every day, we showed that search rankings could boost the proportion of people favoring any candidate by more than 20 percent—more than 60 percent in some demographic groups.

Given how powerful this effect is, it’s possible that Google decided the winner of the Indian election.  Google’s own daily data on election-related search activity (subsequently removed from the Internet, but not before my colleagues and I downloaded the pages) showed that Narendra Modi, the ultimate winner, outscored his rivals in search activity by more than 25 percent for sixty-one consecutive days before the final votes were cast. That high volume of search activity could easily have been generated by higher search rankings for Modi.

Google’s official comment on SEME research is always the same: “Providing relevant answers has been the cornerstone of Google’s approach to search from the very beginning. It would undermine the people’s trust in our results and company if we were to change course.”

Could any comment be more meaningless? How does providing “relevant answers” to election-related questions rule out the possibility of favoring one candidate over another in search rankings? Google’s statement seems far short of a blanket denial that it ever puts its finger on the scales.

There are three credible scenarios under which Google could easily be flipping elections worldwide as you read this:

First, there is the Western Union Scenario: Google’s executives decide which candidate is best for us—and for the company, of course—and they fiddle with search rankings accordingly. There is precedent in the United States for this kind of backroom king-making. Rutherford B. Hayes, the 19th president of the United States, was put into office in part because of strong support by Western Union. In the late 1800s, Western Union had a monopoly on communications in America, and just before the election of 1876, the company did its best to assure that only positive news stories about Hayes appeared in newspapers nationwide. It also shared all the telegrams sent by his opponent’s campaign staff with Hayes’s staff. Perhaps the most effective way to wield political influence in today’s high-tech world is to donate money to a candidate and then to use technology to make sure he or she wins. The technology guarantees the win, and the donation guarantees allegiance, which Google has certainly tapped in recent years with the Obama administration.