It was behind closed doors, but at least it has happened.

Glenn Simpson, the co-founder of GPS Fusion, the firm that put together the controversial Trump oppo-research dossier, testified before the Senate Judiciary Committee in a closed door session on Tuesday.

Today’s questioning was thought to center around funding and sources for the dossier.

Simpson’s firm, Fusion GPS, was first hired by Republicans to dig up dirt on Trump during his presidential campaign. But as Trump emerged as the party’s likely nominee, GOP donors ended their work with the firm, and Democrats began paying Fusion GPS for opposition research on Trump.

Fusion GPS commissioned Christopher Steele, a former British spy, to compile the dossier.

This will tie in to the larger investigation into Russian interference in the 2016 election. It is believed that Russia favored Trump over Clinton for several reasons.

First of all, Trump is malleable. As an inexperienced reality TV huckster, with little to no understanding of how governments operate, diplomatic standards, or basically anything that would make him a wise choice for a nation that actually wants to survive, he was a dream come true for Russia.

His man-crush on Putin was also a bonus.

The idea that there may be embarrassing or compromising footage of Trump in the hands of the Russian government makes him at risk for blackmail, as well. That’s something the Senate Judiciary Committee are keenly interested in.

Simpson had initially declined to speak with the committee but agreed to do so last month. In exchange for his testimony, the panel’s top lawmakers, Sens. Chuck Grassley (R-Iowa) and Dianne Feinstein (D-Calif.), agreed to withdraw a subpoena for his testimony.

According to a Fox News report, Fusion GPS has already turned over some 40,000 documents to the judiciary committee.

The dossier first came to light days before the inauguration, when Buzzfeed News released unsubstantiated details, which included romps in hotel rooms with Russian prostitutes.