Director of National Intelligence James Clapper said Thursday "there is a there there" after reports Robert Mueller has impaneled a grand jury and hired more staff in the Russia probe.
"I don't find surprising this development given this long period which the special counsel has been at work," Clapper, who served in the Obama White House, told Erin Burnett on CNN.
"I also read into it that when Bob Mueller hired more staff, that there is a there there," he added, "but I can't say anything more than that."
Mueller was named to head the probe by the Justice Department in May after President Donald Trump fired FBI Director James Comey.
The Russia probe began under Comey last year.
However, "in the end, if he determines there is no there there, he'll make that call," Clapper said.
"I have no doubt about his integrity, particularly in a matter as sensitive as this."
As such, Clapper said, the investigation has "sort of come full circle" with reports Mueller is also probing the financial ties of the president and his associates.
"My understanding is back in the summer of '16, this all started with questions about financial dealings of trump associates," Clapper told Burnett. "That's how this all began.
"It appears to have come, again, with what's been out in the media – sort of come full circle now.
"But I don't see how you exclude or insulate financial dealings here from the investigation."
Trump warned Mueller in an interview with The New York Times last month he would be crossing a red line in probing his family's finances.
"I'm not sure how someone who is under potential investigation draws red lines and says that certain aspects are out-of-bounds," Clapper said.
"I don't know how that works."