The Post's Ruth Marcus explains why Donald Trump Jr. is in legal jeopardy. Hint: stupidity is not a legal defense. (Adriana Usero,Kate Woodsome/The Washington Post)

This week’s revelations about Donald Trump Jr.’s meeting with a Russian lawyer have shined a new spotlight on a small Washington opposition research firm that worked with her on a legal case for years and then subsequently commissioned a dossier full of salacious allegations of the Russian government’s attempts to collude with the Trump presidential campaign.

The firm, Fusion GPS, will be one subject of a Senate Judiciary Committee hearing next week that was planned well before the story broke of Trump Jr.’s June 2016 meeting with Russian lawyer Natalia Veselnitskaya. Fusion GPS says it had no involvement in the meeting although it did work on a lawsuit that involved Veselnitskaya for more than two years. The firm’s work on the Trump dossier was on a different timeline. Nevertheless, Trump’s legal team is already conflating the two issues as part of their defense of the president’s son.

Emails released Tuesday by Trump Jr. reveal that his friend Rob Goldstone pitched the meeting based on the promise of damning information on Hillary Clinton that supposedly was being offered by senior Russian government officials. On Monday, Mark Corallo, a spokesman for President Trump’s outside counsel, alleged that the meeting had been set up under false pretenses and implied that Veselnitskaya’s association with Fusion GPS was relevant to the alleged deception.

“Specifically, we have learned that the person who sought the meeting is associated with Fusion GPS, a firm which according to public reports, was retained by Democratic operatives to develop opposition research on the president and which commissioned the phony Steele dossier,” Corallo said in a statement.

Even before Trump’s legal team suggested the Veselnitskaya meeting was a dirty trick to set up the younger Trump, pro-Trump media outlets had been calling on federal and Senate investigators to look into the activities of the firm, which is run by two former journalists and has done research for both Republicans and Democrats alike.

Senate Judiciary Committee Chairman Charles E. Grassley (R-Iowa) has been pressing the Justice Department to follow up on a complaint, which is posted on Grassley’s website, alleging that the firm and others violated the Foreign Agents Registration Act by not filing disclosures required when representing foreign entities.

Grassley has scheduled an as yet unannounced hearing July 19 entitled, “Oversight of the Justice Department’s (Non) enforcement of the Foreign Agents Registration Act,” which will include testimony from William Browder, the chief of Hermitage Capital, who filed the complaint against Fusion GPS and several other entities he alleges were working on behalf of the Russians.

Committee sources cautioned that the date and witness list for the hearing is not final until announced. On Tuesday, ranking Democrat Dianne Feinstein (Calif.) publicly called on Trump Jr. to testify before the committee. As of now, the committee is only planning to hear from Justice Department officials and Browder on separate panels.

Browder told me the he will testify that the fact Veselnitskaya was trying to convince Trump campaign officials and family members to change U.S. policy on Russia clearly shows she was acting as an agent of the Russian government.

Veselnitskaya has been a major detractor of the Magnitsky Act, a law that penalizes Russian officials accused of participating in the detention and subsequent death of Sergei Magnitsky. Magnitsky, who died in detention after being severely beaten, was Browder’s lawyer and had uncovered a $230 million tax fraud scheme perpetrated by Russian authorities.

“Repealing the Magnitsky Act was the single biggest priority of Vladimir Putin and she was acting as the single most active proxy of the Russian government to achieve that objective in Washington,” Browder said. “I’m sure that this was an attempt by the Russian government to repeal sanctions that annoyed them by going to the possible next president of the United States.”

Fusion GPS has said that it was working for the law firm BakerHostetler, which was representing Prevezon, a Russian holding company based in Cyprus, in its defense against Justice Department allegations that Prevezon laundered money stolen in the fraud Magnitsky uncovered. Veselnitskaya was Prevezon’s lawyer. Fusion GPS started working on the case in 2013 and the case settled in May with no admission of guilt by Prevezon.

Fusion GPS told me its work on the Prevezon case had nothing to do with the 2016 presidential election and they were not involved in the outreach to the Trump campaign.

“Fusion GPS learned about this meeting from news reports and had no prior knowledge of it,” the company told me in a statement. “Any claim that Fusion GPS arranged or facilitated this meeting in any way is false.”

As a subcontractor for BakerHostetler, Fusion GPS would not have been required to register under FARA. Senators may want to know why BakerHostetler decided that it did not need to register. Neither Veselnitskaya nor Mark Cymrot of BakerHostetler, who handled the Prevezon case, responded to requests for comment.

Regardless, senators on the committee may now use the FARA hearing to press Justice Department officials on what they know about Veselnitskaya, Prevezon, Fusion GPS and their connections to both the Trump campaign or the Russian government.

Prevezon is owned by Russian businessman Denis Katsyv. His father, Pyotr Katsyv, was vice premier and minister of transport of Moscow region from 2004 to 2012. Katsyv’s deputy minister was Alexander Mitusov, Veselnitskaya’s ex husband.

Fusion GPS began its separate work on the Trump-Russia connections in October 2015, working for unnamed Republican clients. After Trump won the primary, Democratic funders continued to push the effort. Christopher Steele, the former MI6 officer who compiled the dossier, was brought on in May 2016.

There’s no evidence that the work Fusion GPS did for BakerHostetler on behalf of Prevezon and their work on the Trump dossier were connected. In fact, the former seems to advance Russian interests while the latter is hugely problematic for the Russian government. It’s entirely possible that the firm was working on two separate Russia-related projects for clients who had opposing interests, roughly at the same time.

If the Trump team continues to allege the two cases are related, the congressional and perhaps federal inquiries into the firm could be just getting started. And Veselnitskaya’s meeting with Donald Trump Jr. is not mentioned in the dossier the firm produced for its American political clients.