The investigation into Nancy Guthrie’s disappearance has faced a devastating blow as authorities have scaled back efforts 100 days after Savannah Guthrie’s mom went missing, experts believe.

“They have definitely scaled back resources in this continuing phase,” retired FBI agent Jason Pack exclusively told Page Six. “That happens in every case. Add resources at the front end to make sure they can cover what needs to be covered.”

Pack went on to explain how the initial response phase “likely had a few hundred agents and officers” compared to “a few dozen” at this point in the investigation.

“Lots of leads initially with the tip line… as it falls out of the news cycle, fewer tips come,” the former FBI agent explained.

Former CIA member and FBI special agent Tracy Walder also believes resources have been scaled back — theorizing how the investigation has turned from “rescue” to “recovery.”

“The investigation is not a rescue investigation,” Walder, who is also a NewsNation contributor, said. “If it’s a rescue … then you are going to have more resources thrown at that because you have a living human that can potentially be recovered.

“At this point, they look at it as a recovery and investigating a crime. There is not a sense of urgency. There is not a risk to the public,” Walder added. “This was specifically targeted towards her. If they thought there was a risk to the public, there would be more urgency.”

Walder said she is “not surprised” Nancy has not been recovered by the 100-day mark, as the kidnapper had a “9 to 10-hour head start.”

Nancy was reported missing from her Arizona home on Sunday, Feb. 1, after she failed to attend a virtual church service. She was last seen on Jan. 31 when her family dropped her off at home after dinner.

Authorities released video and photos of a masked individual breaking into her home on Feb. 10.

In April, it was reported that a hair sample had been sent for DNA testing.

“In this case, we have the hair clipping that has been sent off. … I would like to think we would have a result by now,” Walder said. “I think the fact there is zero digital evidence. The fact that there is no camera along the highway or road that caught a vehicle or a vehicle’s license plate. … In this case, it seems like there is nothing. … I think that’s the piece that’s troubling.”

A spokesperson for the Pima County Sheriff’s Office told Page Six in a statement, “The Pima County Sheriff’s Department remains fully committed to the investigation into Nancy Guthrie’s disappearance. This is an active and ongoing investigation, and we continue to work closely with our partners at the FBI.

“DNA and video analysis are underway, supported by laboratories across the country. Advances in technology are aiding investigative efforts, and tips continue to be received and reviewed.”

Walder said of the Pima County Sheriff’s Office’s statement, “I think that they’re doing what they’re supposed to be doing in my opinion. I think they are just exhausting all options.”

Walder said authorities’ next steps should be genealogical sequencing — which is tracing DNA to family history — finding license plates going in and out of her home area, and more.

“I do [think she’ll be recovered],” Walder said. “I don’t know it will happen overnight. I would like to think it will happen. I will be optimistic.”

Pack added, “It only takes one tip. Someone knows the person in the video. Someone knows what happened.”

Savannah, 54, posted a heartbreaking tribute to Nancy, 84, on Instagram Sunday in honor of Mother’s Day.

“Mother, daughter, sister, Nonie – we miss you with every breath,” she captioned a video collage of her beloved mom. “We will never stop looking for you. We will never be at peace until we find you.”

She then urged her Instagram followers to “help,” as “someone knows something that can make the difference.”

The “Today” anchor added, “Please keep praying. Bring her home.”

Savannah returned to “Today” on April 6 in an emotional welcome back by her co-anchors and viewers.

On Monday, Savannah announced on the morning show that she will host the “Wordle” game show, whose executive producer is Jimmy Fallon.

“We’ve been holding in a secret between us for a long time now,” she said on today’s episode of the game show, which was first reported in October.

“When everything happened with me and my family they just stopped everything and said, ‘We’ll wait for you.’ Hollywood is, like, a really tough business, and I didn’t expect that. And I just want to say thank you, it means so much to me,” she said.

Savannah added, “Everything is strange right now. It’s strange to get up and do the ‘Today’ show every day, and it’s strange to say that I’m going to do a game show when your heart is broken. Nothing about that has changed, and it’s not easy, but I’m determined to put one foot in front of the other.”