WASHINGTON — The special counsel’s accusation this week that Paul Manafort, President Trump’s former campaign chairman, tried to tamper with potential witnesses originated with two veteran journalists who turned on Mr. Manafort after working closely with him to prop up the former Russia-aligned president of Ukraine, interviews and documents show.

The two journalists, who helped lead a project to which prosecutors say Mr. Manafort funneled more than $2 million from overseas accounts, are the latest in a series of onetime Manafort business partners who have provided damaging evidence to Robert S. Mueller III, the special counsel investigating Russian meddling in the 2016 election. Their cooperation with the government has increasingly isolated Mr. Manafort as he awaits trial on charges of violating financial, tax and federal lobbying disclosure laws.

Mr. Manafort’s associates say he feels betrayed by the former business partners, to whom he collectively steered millions of dollars over the years for consulting, lobbying and legal work intended to bolster the reputation of Viktor F. Yanukovych, the former president of Ukraine. Mr. Manafort has told associates that he believes Mr. Mueller’s team is using the business partners to pressure him to flip on Mr. Trump in a manner similar to the one used to prosecute the energy giant Enron in the early 2000s by a Justice Department task force that included some lawyers now serving on Mr. Mueller’s team.

“Anybody who is a student of the Enron prosecution sees a very close parallel,” said Michael R. Caputo, a former Trump campaign operative, who has known Mr. Manafort for three decades and spoke with him on Wednesday. Another associate said Mr. Manafort and some of his close allies were reading a book by the conservative lawyer and commentator Sidney Powell that claims misconduct in the Enron prosecution. And Mr. Caputo, who was interviewed by Mr. Mueller’s team last month, said that “when Paul decided to fight, he knew the lay of the land.”