By manipulating its search results, Google could decide the next election.

The world's most-used search engine is so powerful and national elections are so tight, that even a tiny tweak in Google's (GOOGL) secret algorithm could swing the 2016 presidential election, according to Robert Epstein, senior research psychologist at the American Institute for Behavioral Research and Technology.

In an op-ed on Politico.com, Epstein said that he and a team of researchers studied behavior in undecided voters who had been exposed to rigged search results. By displaying results that shone a more favorable light on a particular candidate the researchers could shift opinion towards that favored candidate.

The study boosted a candidate's favorability rating by between 37% and 63% after just one 15-minute search session. The five double-blind, randomized studies included 4,500 undecided voters in the United States and India.

A Google spokeswoman said that the company's algorithm is designed to provide "relevant answers," and rigging them to favor one view over another "would undermine the people's trust in our results and company."

Epstein said Google's response was "meaningless."

"How does providing 'relevant answers' to election-related questions rule out the possibility of favoring one candidate over another in search rankings? Epstein wrote in his op-ed. "Google's statement seems far short of a blanket denial that it ever puts its finger on the scales."

The research suggested that swinging an election was "well within Google's control," considering that President Obama won the 2012 election by just 3.9% and the 2016 polling is similarly too close to call.

Though Epstein falls short of saying that Google would rig an election, he points to historical precedent suggesting that Google wouldn't be alone if it tried.

Epstein pointed to Western Union's attempt to swing the 1876 presidential election towards its favored candidate, Rutherford B. Hayes. The election was the closest in U.S. history, and Western Union used its telegraph network monopoly and exclusive carriage contract with the Associated Press to ensure that only positive stories about Hayes made it on the wire. Hayes ultimately won by a hair.

On average, Google adjusts its algorithm more than once a day. Epstein said it's possible that even if the Alphabet triumvirate of Larry Page, Sergey Brin and Eric Schmidt didn't get directly involved in tipping the scales on an election, a rogue employee could tweak the code without the leaders' knowledge.

"Google could easily be flipping elections worldwide as you read this," Epstein said.