The main events in a political campaign used to happen in the open: a debate, the release of a major TV ad or a public event where candidates tried to earn a spot on the evening news or the next day's front page.
That was before the explosion of Facebook, Twitter and YouTube as political platforms. Now some of a campaign's most pivotal efforts happen in the often-murky world of social media, where ads can be targeted to ever-narrower slices of the electorate and run continuously with no disclosure of who is paying for them. Reporters cannot easily discern what voters are seeing, and hoaxes and forgeries spread instantaneously.
Journalists trying to hold candidates accountable have a hard time keeping up.
"There's a whole dark area of campaigns out there when, if you're not part of the target group, you don't know anything about them," said Larry Noble of the Campaign Legal Center in Washington, which seeks greater transparency in political spending. "And if reporters don't know about it, they can't ask questions about it."
The problem came to widespread attention during the 2016 presidential race, when Donald Trump's campaign invested heavily in digital advertising, and the term "fake news" emerged to describe pro-Trump propaganda masquerading as online news. Russian interference in the campaign included covert ads on social media and phony Facebook groups pumping out falsehoods.
The misinformation shows no sign of abating. The U.S. Senate election in Alabama in December was rife with fake online reports in support of Republican Roy Moore, who eventually lost to Democrat Doug Jones amid allegations that Moore had sexual contact with teenagers when he was a prosecutor in his 30s. Moore denied the accusations.
Politicians also try to create their own news operations. U.S. Rep. Devin Nunes' campaign funded a purported news site called The California Republican, and the executive director of Maine's Republican party last month acknowledged that he runs an anonymous website that is critical of Democrats.
Phony allegations are nothing new in politics. But they used to circulate in automated phone calls, mailers that were often tossed in the trash or, as far back as the 1800s, in partisan newspapers that published just once a day, noted Garlin Gilchrist, executive director of the Center for Social Media Responsibility at the University of Michigan.
The difference now is how quickly false information spreads.
"The problem is something that's always existed ... but social media is a different animal than news distribution in the past," Gilchrist said.
A study released this past week found that false information spreads faster and wider on Twitter than real news stories. Researchers at the Massachusetts Institute of Technology traced the path of more than 126,000 stories on Twitter and found that the average false story takes about 10 hours to reach 1,500 users compared with about 60 hours for real ones. On average, false information reaches 35 percent more people than true news.
A data analysis by Buzzfeed's news site after the 2016 election found that the most popular fake stories generated greater engagement on Facebook than the top real stories in the three months before Election Day.
Because it's increasingly easy to fabricate videos, which are viewed as the most reliable evidence available online, reporters "need stronger tools" to weed out frauds, Gilchrist said.
Social media also upends campaign advertising practices. Federal regulations require a record of every political advertisement that is broadcast on television and radio. But online ads have no comparable requirements.
Earlier this month, Twitter Chief Executive Officer Jack Dorsey announced that the platform would take new steps to try to stop harassment and false information. Facebook has partnered with media organizations, including The Associated Press, to flag false information on its platform. It recently announced plans to reform its political advertising, including making all ads on a page visible to all viewers, regardless of whether they were intended to see the spots. It also will require a line identifying the buyer on every political ad and create a four-year archive.
Still, because there are so many candidates for office in the U.S., Facebook is limiting itself to federal races at first.
"Facebook is moving faster than regulators are around the world toward some better stuff," said Sam Jeffers of the UK-based group Who Targets You, which pushes for better online campaign disclosure.
He cited three recent elections in which underdog campaigns invested heavily in online ads and beat the polling expectations to win: the 2015 parliamentary races and the Brexit vote and the U.S. presidential race the following year.
Who Targets You designed an online tool that will collect Facebook political ads and deposit them in a database.
In the U.S., the nonprofit investigative outlet ProPublica has a similar project underway with a widget called Political Ad Tracker, which can be downloaded by readers to build a database of online ads. Other organizations, including the AP, have begun publishing stories specifically intended to knock down false information circulating on social media.
Some efforts are more local. In Seattle's municipal election last year, online ad spending increased 5,000 percent over the previous cycle in 2013. Eli Sanders, a reporter for the alternative weekly The Stranger, unearthed a city ordinance that requires any outlet that distributes a political ad to make copies available for public inspection. His reporting inspired the city's ethics and elections commission to demand the data from online outlets.
Google and Facebook have shared some fragmentary information with the Seattle commission, and through them Sanders is getting his own window into the online political marketplace. One outside group that supported the candidate who won the mayoral election, Jenny A. Durkan, spent $20,000 on one ad on a Google platform that the company displayed between 1 million and 5 million times.
"Just like at the national level, locally there is this whole segment of political advertising that is not transparent," Sanders said.