Steve Bannon, former White House Chief Strategist to U.S. President Donald Trump Getty Images

Steve Bannon has a warning for candidates supported by the conservative Koch political donor network – just ahead of crucial midterm elections this fall. "You take Koch money, it's going to be toxic. We are going to let people know that if you take Koch money there's a punishment," Bannon, former chief White House strategist and Trump campaign chief executive, told CNBC in an exclusive interview. "If you take money from people who are against the president and are looking to put a knife in the back of the president, you are going to pay." The strategist declined to elaborate on what the punishment would look like. The Koch network traditionally backs Republican candidates, but has recently said it is open to supporting Democrats who favor the group's policies. Bannon's threat came hours after President Donald Trump fired back at the Koch network, which has intensified its criticism of the administration's policies in recent days. A Koch-linked group unveiled an ad buy targeting Trump's hard-line trade policies during a weekend summit. "The globalist Koch Brothers, who have become a total joke in real Republican circles, are against Strong Borders and Powerful Trade," the president said in a two-tweet tirade early Tuesday. "I have never sought their support because I don't need their money or bad ideas."

While the billionaire Kochs favored Trump's tax cuts and deregulation, their political organization has taken aim at the president's immigration and tariff policies. The group also criticized a $1.3 trillion spending bill the president signed earlier this year. Bannon, in an interview with Politico that ran over the weekend, had urged the Kochs to "shut up and get with a program" in backing Trump's agenda in this fall's midterm elections. But on Tuesday, he ratcheted up his already-heated rhetoric. "Let's start holding the Kochs accountable. It's a con job and they are a total scam," Bannon said Tuesday. "They are promoters and it's a total Ponzi scheme. They never raise as much money as they talk about and no one ever knows who their donors are." James Davis, a spokesman for the Koch network, responded to Bannon's criticism in a statement Tuesday. "We are focused on uniting the country to help remove barriers that are preventing people from reaching their potential, and we look forward to working with anyone to help people improve their lives," Davis said.

A sharp divide

Bannon said he doesn't believe the widely influential Koch organization is as powerful as it used to be. His political operation, he said, will go on a "continual pressure" campaign against the Koch network, its donors and any candidate who accepts money from the organization. "We are going to find out who they [the donors] are. We are going to identify people who the Kochs back. We're not just going to sit there and allow them to destroy the Trump presidency," Bannon said. The outrage from Trump and Bannon came after Koch network officials told financial backers at a summit over the weekend that they are no longer committed to solely backing Republican candidates in this year's congressional midterm elections. The group said it is leaving the door open to potentially supporting Democrats who back their policy initiatives. "I know this is uncomfortable," Emily Seidel, chief executive officer of Americans for Prosperity, told a group of donors on Sunday. "If you are a Democrat and stand up to [Sen.] Elizabeth Warren to corral enough votes for financial reform that breaks barriers for community banks and families, you're darn right we will work with you." Charles Koch himself told reporters that he hopes to see people in power who will back policies that will "move toward a society, mutual benefit, equal rights, where everybody has the opportunity to realize their full potential." He added, "I don't care what initials are in front or after somebody's name." On Monday, the network announced that it wasn't planning to back Rep. Kevin Cramer, R-N.D., against Democratic Sen. Heidi Heitkamp in a race Republicans see as a prime opportunity for a Senate seat pickup. Bannon said the Koch network has received everything it has wanted from the Trump administration, including comprehensive tax reform, business deregulation and conservative Supreme Court justices, including the recent nomination of Judge Brett Kavanaugh. Yet, he said, none of that matters to the Kochs because they didn't support Trump during the election.

Bannon stays on Trump's side