The co-founder of a Washington opposition research firm that produced a dossier of salacious allegations involving President Donald Trump is set to speak behind closed doors to congressional investigators.

Glenn Simpson is expected to appear privately Tuesday before the Senate Judiciary Committee for a transcribed interview.

Simpson runs Fusion GPS. That firm hired the British intelligence officer who produced the dossier containing allegations of ties between Trump and Russia.

The Senate committee is one of several investigating Russia’s interference in the 2016 election and any possible collusion with Trump associates.

The committee this month disclosed that it had received tens of thousands of pages of documents as part of its investigation.
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