Former New Jersey Gov. Chris Christie said the Southern District of New York presents more of a “problem and a threat” to President Donald Trump than special counsel Robert Mueller’s investigation.

While Mueller can only investigate potential collusion with Russia during the 2016 presidential campaign, the SDNY has no limit to the scope of what they can investigate.

“I always said that Bob Mueller is not what should concern the President or the White House. That’s the Southern District of New York,” said Christie, speaking to CNN‘s Chris Cuomo Thursday night.

Aside from the lack of limitations, Christie said the SDNY could benefit from Trump’s former personal lawyer Michael Cohen and Trump’s deputy campaign chairman Rick Gates, both of whom could act as “tour guides” through Trump’s “business and personal life.”

When testifying before Congress this week, Cohen said he couldn’t discuss certain subjects in regards to Trump’s alleged wrongdoing due to ongoing SDNY investigations. He added that he’s in “constant contact” with the office regarding these investigations.

Christie said that while he doesn’t believe the SDNY has a case against Trump “at the moment,” they’re very likely building a case against those around him. They could also be building a case against Trump for when he leaves office, but the statute of limitations is likely to be up for many of these charges, said Christie.

“The fight that’s going to happen now, I think, is between Congress and the Southern District of New York,” said Christie, arguing that Congress is going to want to interrogate more of Trump’s associates, including his children and Allen Weisselberg, chief financial officer of The Trump Organization. These people could negotiate for immunity in exchange for speaking to Congress.

“The Southern District of New York, I can guarantee, is not going to want that,” said Christie. “They’re trying to build a case.”