Has this been debunked and how?

Explained What Started the Trump-Russia Investigation? Not the Steele Dossier as Trump Claims

Republican memo released in February affirmed a story from the New York Times which traces the beginning of the investigation into the Trump campaign's ties to Russia to campaign aide George Papadopoulos

Haaretz and Reuters Aug 12, 2018 3:35 PM

https://www.haaretz.com/us-news/what-started-the-trump-russia-investigation-1.5788518

U.S. President Donald Trump continues to argue on Twitter that the Steele Dossier, which was paid for Hillary Clinton's presidential campaign is what started the special counsel Russia investigation - but in reality it had begun before the Steele Dossier was made public.