‘‘The issue of collusion is still open,’’ said the Republican committee chairman, North Carolina Senator Richard Burr, who along with the panel’s top Democrat, Virginia Senator Mark Warner, provided the first major update on a congressional investigation that was launched the same month as President Trump was inaugurated.
‘‘The committee continues to look at all evidence to see if there was any hint of collusion,’’ Burr said, adding that ‘‘I am not going to even discuss initial findings, because we haven’t any.’’
Burr and Warner said that the committee has interviewed more than 100 witnesses, including former Trump campaign chairman Paul Manafort and Trump son-in-law Jared Kushner. More than 100,000 pages of documents have been reviewed.
But the committee has still yet to interview some witnesses related to the Trump campaign and a June 2016 meeting that Kushner, Manafort and the president’s son, Donald Trump Jr., held with Russians. The committee wants to interview everyone involved with the meeting.
The lawmakers said that though they have reached no conclusion about whether the campaign colluded with the Kremlin — the question also at the heart of a separate criminal investigation by special counsel Robert Mueller — their investigation has left no doubt about a multi-pronged Russian effort to meddle in American politics.
‘‘The Russian intelligence service is determined, clever, and I recommend every campaign and every election official take this very seriously,’’ Burr said.
The news conference Wednesday was an effort by the committee to lay out some of what’s been found so far as the 2018 midterm elections approach. Burr said that the committee would ideally finish the investigation before congressional primaries begin next spring, but said he couldn’t put a firm deadline on the probe because they are always finding new lines of inquiry.
Warner said there is a ‘‘large consensus’’ that Russians had hacked into political files and strategically released them with the goal of influencing the election. He said Russian hackers had also tested the vulnerabilities of election systems in 21 states, though there’s no evidence that any voting tallies were altered.
The Senate panel has also been focused on Russian efforts to push out social media messages on Twitter and Facebook, and is examining more than 3,000 Russia-linked ads that
Facebook turned over to Congress this week. Burr said he does not intend to release those ads.
Facebook has said the ads focused on divisive social and political messages, including
LGBT issues, immigration, and gun rights, and were seen by an estimated 10 million people before and after the 2016 election.
The Senate panel, along with the House intelligence committee, has invited Facebook, Twitter, and Google officials to testify at a public hearing next month.
One witness the lawmakers say they’ve been unable to question is Christopher Steele, a former British spy believed to have compiled a dossier of allegations about Trump connections to Russia. Burr said the committee ‘‘has hit a wall’’ in its requests to interview Steele, as he has not accepted offers to meet with staff or with Burr and Warner personally.
‘‘The committee cannot really decide the credibility of the dossier without understanding things like who paid for it, who are your sources and subsources?’’ Burr said.
‘The Russian intel-igence service is determined, clever, and I recommend [that every campaign . . . take this very seriously.’
Burr said he was pleading to Steele directly to talk to the committee.
‘‘My hope is that Mr. Steele will make a decision to meet with either Mark or I, or the committee or both so we can hear his side of it,’’ he told reporters, adding: ‘‘I say that to you but I also say it to Mr. Steele.’’
Burr said the panel has 25 more witnesses scheduled this month. He threatened any future witnesses who may balk at the committee’s invitations with subpoenas.