Donald Trump Jr. hasn’t even been summoned to Capitol Hill yet, but already a senator investigating the Trump Team’s ties to Russia considers his explosive meetup with a Kremlin-tied attorney an “attempt at collusion.”

“Based on Donald Trump, Jr.’s own admissions, there was, at a minimum, an effort by the Trump campaign to have the Russians help Donald Trump get elected. That’s an attempt at collusion,” Ron Wyden, an Oregon Democrat on the intelligence committee, told the Daily Beast.

“It absolutely should be part of the investigations into Russia’s meddling in the election.”

The president’s eldest son might be downplaying his June 2016 meeting to discuss dirt on Hillary Clinton with a Russian attorney. But lawmakers of both parties are signaling their intentions to formally interview Trump about it.

Two Republican senators on the intelligence committee have already signaled that they have questions for the eldest Trump son. And the Senate Intelligence Committee’s top Democrat said Monday that he “absolutely” wants to speak with Trump Jr.

And according to a knowledgeable congressional staffer, Democrats on the House intelligence committee are preparing a strategy session, likely ahead of a closed-door session of the full panel on Tuesday, to discuss pushing their inquiry to add Trump Jr. to the witness list.

The June 9, 2016 meeting between Russian attorney Natalia Veselnitskaya and a bevy of Trump-campaign officials—Don Jr., Jared Kushner, and former campaign chief Paul Manafort among them—presents some of the strongest evidence yet of collusion with the Kremlin, a charge the elder Trump has vociferously denied. Though Donald Trump Jr. has shifted his explanations of the meeting, on Sunday he said in a statement that the Kremlin-connected Veselnitskaya provided “no details or supporting information.”

But Trump Jr. made clear that he took the meeting with the expectation that she would provide “potentially helpful information” to the campaign. He reportedly has now hired an attorney, Alan Futerfas, to aid with his expected testimony.

“This is the first time that the public has seen clear evidence of senior-level members of the Trump campaign meeting with Russians to try to obtain information that might hurt the campaign of Hillary Clinton,” Sen. Mark Warner, the vice chairman of the Senate Intelligence Committee, told reporters Monday. He said it follows a pattern of “convenient forgetfulness” among top Trump officials’ meetings with Russians.

“What continues to bother me is this pattern—and I think we’re up to 20-plus examples—of where senior-level Trump officials, and even you could argue the president himself, continue to deny that they’ve had any kind of contacts with Russians, until the proof comes out that there were contacts, multiple contacts, and then these officials recant or amend their filings,” Warner said.

A source close to the Senate Intelligence Committee’s parallel inquiry into the Trump-Russia connection said that everyone involved in the meeting with Veselnitskaya, an advocate for rolling back sanctions on Russian human-rights abuses, would be questioned.

“Of course they’ll ask Kushner, Manafort and Don Jr. about this. Nothing is more central to the investigation,” said the source.

The younger Trump took the June 9 meeting at Trump Tower, he said, at the behest of a music publicist, Rob Goldstone, whom he met during the 2013 Miss Universe pageant the Trumps held in Moscow. Goldstone told the AP on Monday that he tapped Trump Jr. for the meet with Veselnitskaya at the behest of his client, Russian singer Emin Agalarov. Agalarov’s father Aras is an oligarch whom the Washington Post reported last year “served as a liaison between Trump and the Russian leader” Vladimir Putin for the pageant, which the elder Agalarov and a group of investors underwrote.

During the 2013 beauty pageant, Emin Agalarov got Trump to make a cameo appearance in a pageant-themed music video.

The day that Trump Jr., Kushner, and Manafort met with Veselnitskaya, Trump tweeted a reference to Clinton’s 33,000 missing emails, which the following month he would publicly implore Russia “to find the 30,000 emails that are missing.”

Meanwhile, the House is not the only venue trying to learn what happened at the June 9 parley.

“We’re trying to be able to get further details” on the meeting, Oklahoma Republican James Lankford, a member of the Senate Intelligence Committee investigating the Trump-Russia question, told NPR on Monday. His GOP colleague on the panel, Susan Collins of Maine, said she wants all three Trump-campaign attendees queried about it.

Lankford added that Kushner disclosed the meeting with Veselnitskaya in his security clearance form, but Warner declined to say whether the committee knew the meeting took place before it was publicly reported. The vice chairman also declined to say whether the committee had already reached out to Trump Jr., or if the committee was aware of any similar meetings where top campaign officials were seeking information from Russians.

With the Senate panel expected to interview Team Trump members as early as this week for its probe, a source close to the investigation said the committee would doubtlessly focus on the Veselnitskaya meeting with its attendees.

Adam Schiff, the top Democrat on the House intelligence committee, told CNN Sunday, “I think we're going to want to question everyone that was at that meeting about what was discussed.” A Schiff representative would not elaborate on potential or actual witnesses as a matter of policy.

Eric Swalwell, a California Democrat who serves on the House intelligence committee, told The Daily Beast on Sunday that “each of those ties, including recently learned meetings between Don Jr., Jared Kushner, and Paul Manafort with Russians who wanted to damage Hillary Clinton, must be fully investigated.”

Lankford said the Senate “absolutely” should examine the meeting, but drew a line short of considering it evidence collusion with Russia.

“This is the Russians reaching out through some of their third parties,” Lankford said Monday on NPR.

“We need to be able to find out how they were doing it and why they were doing it. But just because a meeting occurred doesn’t necessarily mean the campaigns cooperated together.”