The Guardian published an article April 13th titled, “British spies were first to spot Trump team’s links with Russia.”  It concludes with a gripping statement.

One source suggested the official investigation was making progress. “They now have specific concrete and corroborative evidence of collusion,” the source said. “This is between people in the Trump campaign and agents of [Russian] influence relating to the use of hacked material.”

The article does not identify the source.  But just before the last paragraph quoted above, the article states,

Adam Schiff, the senior Democrat on the House committee, has expressed an interest in hearing from Christopher Steele, the former MI6 officer whose dossier accuses the president of long-term cooperation with Vladimir Putin’s Moscow. Trump and Putin have both dismissed the dossier as fake.

Schiff has stated on the record there is “more than circumstantial evidence of collusion.”  He said this to Chuck Todd on national TV March 22nd.