Intelligence experts say Russian outreach to the Trump campaign fits the pattern of an intelligence operation.
Former officials have reviewed the attempts by Russians to establish contact as laid out in recent court filings by special counsel Robert Mueller. They conclude they were apparently targeted and more frequent than would be expected during a typical presidential campaign.
Mueller has been investigating Russian interference in the 2016 presidential election for more than a year and has not revealed clear evidence of coordination between the Trump campaign and the Kremlin.
Much of the investigation is still under wraps.
Court filings from Mueller show Russian contacts with the Trump campaign began within months of Trump announcing his candidacy in June 2015.