Like dandelions in an untreated lawn, the now infamous Russian dossier apparently multiplied in numbers — and emissaries delivering it to the FBI — the closer Donald Trump got to the White House.

We know from public testimony that dossier author and former British intelligence agent Christopher Steele shared his findings with the FBI in summer and fall 2016 before he was terminated as a confidential source for inappropriate media contacts.

And we learned that Sen. John McCain (R-Ariz.) provided a copy to the FBI after the November 2016 election — out of a sense of duty, his office says.

Now, memos the FBI is turning over to Congress show the bureau possessed at least three versions of the dossier and its mostly unverified allegations of collusion.

Each arrived from a different messenger: McCain, Mother Jones reporter David Corn, Fusion GPS founder (and Steele boss) Glenn Simpson.

That revelation is in an email that disgraced FBI counterintelligence agent Peter Strzok wrote to FBI executives around the time BuzzFeed published a version of the dossier on Jan. 10, 2017.

“Our internal system is blocking the site,” Strzok wrote of the document posted on BuzzFeed. “I have the PDF via iPhone but it’s 25.6MB. Comparing now. The set is only identical to what McCain had. (it has differences from what was given to us by Corn and Simpson.)”

The significance of Strzok’s email is obvious to investigators who reviewed it in recent days. The FBI is supposed to be immune to manipulation by circular information flows, especially with sensitive investigations such as evaluating whether a foreign power tampered with an American election.

Yet, in this case, the generally same information kept walking through the FBI’s door for months — recycled each time by a new character with ties to Hillary Clinton or hatred for Trump — until someone decided they had to act.

That someone was Strzok, whose own anti-Trump bias was laid bare by his personal text messages. He first opened a case on Russia-Trump collusion on July 31, 2016 after the first flow of information, then escalated to get a warrant targeting a former Trump adviser in October after a second flurry of allegations.

The pattern is so troubling that one investigator said this to me: “The dossier and its related dirt was on a circular flight path aboard a courier service called ‘Air Clinton,’ and the FBI kept signing for the packages.”

Here is the evidence that supports those concerns.