 -- No one – not even President Trump’s children – will be off limits as Congress starts to investigate purported contacts between the Trump campaign and Russian officials.

“I don't think anyone is beyond the scope of what we need to look at,” said Rep. Adam Schiff (D-CA), the ranking Democrat on the House Permanent Select Committee on Intelligence, when asked whether the probe will look into an October appearance by Donald Trump Jr. at a French think tank with such strong ties to Russia, it nominated Vladimir Putin for a Nobel Peace Prize.

Three weeks before Election Day, Trump flew to Paris to attend a gathering at the Ritz Hotel hosted by the Center of Political and Foreign Affairs (CPFA). The obscure think tank was founded by a wealthy French businessman, known to have deep business in Russia, and his Syrian-born partner, who later told reporters she flew to Moscow and briefed a senior Russian official about the visit with Trump Jr.

The founders, Fabian Baussart and Randa Kassis, did not respond to requests for comment on Trump Jr.’s visit, though a photo of his appearance is featured on the organization’s website.

Schiff said the trip is one of numerous connections documented between Trump campaign advisors and people with close Russian ties.

“The sheer number of meetings that have now been acknowledged by the Trump people, the fact that the Trump people have tried to conceal these meetings, it all begs the question of where is this coming from and why,” Schiff said.

The Trump White House has dismissed questions about the contacts between Russian officials and his campaign aides as routine, and said the criticism about them amounts to a partisan witch hunt.

And a top attorney for the Trump Organization told ABC News Friday that the president’s eldest son was no different than the many other dignitaries from both political parties who have joined the Paris-based organization for a dinner discussions about the topics of the day. He noted that former Clinton advisor James Rubin met with the group a month earlier.

“Donald Trump Jr. has been participating in business related speaking engagements for over a decade – discussing a range of topics including sharing his entrepreneurial experiences and offering career specific advice,” said Alan Garten, the Trump Organization’s executive vice president and chief legal officer. “The CPFA was no different and any suggestion to the contrary is completely unfounded.”

The Trump Organization would not say how much Trump Jr. was paid for the speech, but his speaking agent lists his typical fee as $50,000 or more.

Marcel H. Van Herpen, an expert on the Russian use of front groups, said he does not have any specific research on CPFA, but he believes Trump Jr.’s appearance appears to fit a pattern he documented in his book, "Putin's Propaganda Machine."

“If you consider the important financial means of which they dispose, it is … clear that they have mighty sponsors,” he said.

Schiff said it is too early to know who will be called to testify before the committees investigating allegations that Russia made attempts to influence the 2016 elections.

“We have to look at the evidence, figure out what more we need to find out, who we need to ask to find out what we need to tell the American people we've done a thorough investigation,” he said.