It isn't just one guy, and that is the problem.
There is Steele: The SOLE source of the Russian based intel used to create the FISA request
Nope. Wrong. FALSE!
I have just finished re-reading the Nunes Memo, and nowhere does it assert that Steele is "the SOLE source of the Russian based intel used to create the FISA request." That's a narrative the right wing likes to put forth, but the Nunes Memo pointedly never says that.
In fact, the Russia investigation began with an Australian diplomat reporting to the FBI about bragging done by George Papadopoulos, another Trump advisor approached by Russians.
In fact, Carter Page was on the FBI's radar as early as 2013 due to contacts with Russian spies, spies who were later criminally charged. All along, Page's associates remarked how very pro-Russia he was. After Page joined the Trump campaign, he was invited to Russia for "discussions" and traveled there in July 2016. He got permission from the campaign to go, and reported back to the campaign afterwards about his Russian trip. These reasons, all external to the Steele Dossier, are part of why the FBI sought FISA warrants on Page's international communications.
Please, the assertion that the Russia investigation depends solely on the Steele Dossier is flat out false. And while we're on the subject of the Steele Dossier, it's also false to claim it was entirely funded by the Democrats. That oppo research was originally funded by the Washington Free Beacon, a website funded by major GOP. donor Paul Singer. Singer hired Fusion GPS to do oppo research on several GOP candidates.