Ivanka is 1 Trump spared from DC investigations. But for how long? Investigating the president's daughter could be an optics problem for Democrats.

House Democrats launched their latest investigation into the Trump administration last week by blitzing document requests to 81 individuals and entities linked to the president, but one prominent figure wasn't contacted: Ivanka Trump, his oldest daughter and one of his closest advisers.

Unlike her brothers, Eric and Donald Jr., and her husband, Jared Kushner, Ivanka Trump appears to have remained largely untouched by the state, federal and congressional investigations that have initiated scores of closed-door interviews, grand jury sessions, document demands and hours of sworn testimony on Capitol Hill. But in recent days, congressional Democrats have been expressing growing uncertainty over whether she'll remain out of bounds.

"There's no bar except relevance," said Rep. Adam Schiff, the Democrat leading the House intelligence committee. "If she or any other family member or any other witness is pertinent to our investigation, they don't get a pass."

Ivanka Trump has not been accused of any wrongdoing. She did, however, have visibility into potentially a number of the investigative threads that both Congress and law enforcement have pursued.

Like her husband, there have been questions about her security clearance, especially recently. She was copied on email discussions about a proposed Trump Tower in Moscow. She was a regular presence at her father's side on the campaign trail, including at his Bedminster, New Jersey, club over the weekend during which he decided to fire FBI Director James Comey. And one House aide told ABC News there has been an uptick in interest in the array of global business interests she once ran. She announced a formal leave of absence from her apparel and accessory brands and other private ventures in 2017.

Ivanka Trump has been guarded about weighing in on the investigations into her father. But in an interview with ABC News last month, she objected to the suggestion she received any special treatment with respect to her security clearance, saying she didn't. And she said she "barely" knew about the prospective Moscow deal that the Trump Organization pursued while her father was running for president.

"Literally," she said, "almost nothing."

A spokesman for her lawyer has not yet responded to a request for comment.

Still, speculation about whether she could or should be called to testify on any of these topics has spurred intense debate among Democrats.

A former federal prosecutor told ABC News there would need to be a solid basis for any prosecutor to bring her in to answer questions, and there simply may not be any. Unlike her husband, who attended the now-infamous meeting in Trump Tower with Russians promising dirt on Trump's political opponent, Ivanka Trump's name has not surfaced in connection with any well-known touchstone of the probe, said Renato Mariotti, a former federal prosecutor.

"I understand her last name is Trump, but how is she involved?" Mariotti said.

Another former prosecutor with experience on Capitol Hill, Melanie Sloan, said she believes many congressional advisers have concerns about the optics of calling the president's daughter to Capitol Hill, and the potential political consequences.

"There is a long tradition not going after the children," Sloan said. "By calling her, you are just giving the White House a strong talking point to use against you."

Rep. Gerry Connolly, D-Va., acknowledged that reasoning in a recent interview with Politico.

"Getting to family members, I think, is dangerous," said Connolly, a senior member of the House Oversight and Reform Committee. "It gets real personal, real fast. And it risks backfiring."

Ivanka Trump's absence from the investigative storyline may not last, however. Democrats told ABC News it's possible she could hear from them in the coming weeks.

On Wednesday, House Oversight Committee Chairman Elijah Cummings, D-Md., said he wants to review her security clearance as part of his committee's review of clearance procedures at the White House, including Kushner's.

House Judiciary Committee Chairman Jerry Nadler, D-N.Y., declined to say Thursday why his panel didn't send a letter to Ivanka Trump in its first round of document requests, but didn't rule out doing so later.

"As the investigation goes forward, we'll see who makes sense to interview, to ask for documents from," he added.

House Foreign Affairs Committee Chairman Eliot Engel said his committee could take a closer look at the trademarks China awarded Ivanka Trump for her handbags, jewelry and spa service on April 6, 2017, when she and Kushner sat next to the Chinese president and his wife at Mar-a-Lago during a meeting between the two world leaders.

Democrats previously raised concerns about potential conflicts of interest while in the House minority, and are continuing to study whether the family's business relationships have been affected by changes to U.S. foreign policy.

"It would be [in our jurisdiction], if we choose to make it, but we'll see," Engel said.

Rep. Raja Krishnamoorthi, D-Ill., a member of the House Oversight and Intelligence Committees, said the president's children are not out of bounds.

"As long as they are a material witness to something that's important to the investigation," he said, "I don't think so."