One day after CNN reported that Bernie Sanders allegedly told Elizabeth Warren, in a private meeting in 2018, that a woman could not defeat Donald Trump, a reporter from another TV network trumpeted a different Sanders scoop.

“NEW—Bernie Sanders on House floor in ’98: ‘Saddam Hussein is a brutal dictator who should be overthrown, and his ability to make weapons of destruction must be eliminated,’” tweeted NBC’s Jonathan Allen, with a link to his longer story about the rising tensions between Warren and Sanders. “One of many times he backed regime change in Iraq and elsewhere,” Allen continued, not without glee.

In the story, Allen wrote that Sanders, despite his nearly impeccable anti-war record, “voted repeatedly for a U.S. policy of regime change in Iraq,” citing his votes for the Iraq Liberation Act of 1998 and accusing him of supporting the Clinton administration’s air strikes. These discrepancies were “pointed to by a Democrat familiar with Sanders’ record,” according to Allen, who then quoted from the Vermont senator’s floor speech and noted that “while Sanders’ more mixed record on war and peace hasn’t yet become an issue, it is something that his critics have long talked about that could bubble up at any time.”

If you’re wondering where all this came from and why it matters, welcome to oppo dump season: the most wonderful time in an electoral campaign, when reputations are wrecked, personal lives ruined, and voters misled.

For the journalists who cover politics and the people who work for campaigns, the oppo dump—short for “opposition research dump”—is a tried and true tradition. Despite its power to determine the course of media coverage in campaigns of national and hyperlocal scope alike, it’s not well understood by the public.

Many journalists, content to maintain a certain enigmatic glamor around their profession, don’t like to talk about it, lest it impugn their credentials as investigative watchdogs.

As a practicing journalist, as well as someone who once ran for office, I’ve been on both ends of this process at different times in my career. Campaigns engage in it because they want to win elections. Journalists, however, have a murkier justification.

Here’s how it works. Campaigns, depending on their size and scope, employ researchers to dig into a political opponent’s past. These researchers often do the hard digging that journalists, in an era of shrinking newsrooms, no longer have the time to do. Investigators scour old newspapers, TV and Web archives, social media, and various public records for damning information or ideological inconsistencies. Well-funded campaigns have the resources to do this extensively.

Typically, oppo dumps occur closer to election time, when more voters are paying attention. After the information is found, the campaign must decide which reporter and which media organization to feed it to. Many factors come into play here. Is the outlet respected enough? Can it deliver maximum impact? Almost as important is the reporter. Campaigns don’t necessarily want the best reporter to deliver the scoop. They want one who will tell the story the way they want it told.

The campaign makes a crucial stipulation: no fingerprints! This means the journalist can’t reveal where the dirt came from, creating the illusion that the hit originated with the reporter. After all, there is far more power in a seemingly independent report than in an attack clearly aimed by one candidate at another.

The journalist then takes the scoop with the stipulation, stated or not, that it will be reported in a way the campaign will find favorable. (If it isn’t, the journalist risks losing all access—and future scoops—to rival publications. This is the pitfall of access journalism.)

After the dirt has been reported, the campaign that unearthed it can then condemn the misdeed from afar, embarrassing its opponent.

The CNN report about the Sanders-Warren meeting could have followed this pattern, though we can’t know for sure without the reporter giving up the initial source. It appears a Warren staffer or someone very close to the meeting leaked a version of the comment to CNN, allowing Warren to then confirm a reported story and put Sanders on the defensive. The reality is that we don’t know what truly happened.

With the same caveats, it’s likely that the campaign of one of Sanders’s rivals—Warren, Joe Biden, or even Pete Buttigieg come to mind—fed Allen the clip of Sanders speaking on the House floor. With that reported, the rival got the desired hit on Sanders, and Allen could sleep soundly, knowing that journalism had been done.

Except that it wasn’t the whole story. Lee Fang of The Intercept dug up a longer clip to give more context to Sanders’s speech. In it his “brutal dictator” remark is an aside in a much longer condemnation of the United States’ decision to take military action without congressional approval or international support. “I have serious doubts, however, whether the action that we are taking today will take us one step forward in that direction, and I fear that innocent civilians, that women and children in that country, will be killed,” Sanders said.

Had Allen reported the full context of that speech, it would have made for better journalism, but it would also have violated the assumption of the oppo dump: You report this the way we gave it to you.

Opposition research can, of course, be a foundation of great journalism. But too often reporters are content merely to carry the water of a campaign, creating false impressions for a public already distrustful of the media.