The Senate Judiciary Committee dropped its subpoena to hear from former Trump campaign manager Paul Manafort and request to hear from Donald Trump Jr. in a Wednesday hearing on on foreign lobbyist registration and the Trump dossier, settling for interviews and documents from them instead.

The committee also withdrew a subpoena for Glenn Simpson, the co-founder of the opposition research firm Fusion GPS, which hired spy Christopher Steele to compile a dossier with negative -- if unsubstantiated -- information on Donald Trump's ties to Russia. Amid the multiple probes of Russian interference in the 2016 election and any ties between Russia and the Trump campaign, Senate Judiciary Chairman Chuck Grassley, R-Iowa, on Wednesday dove into the Foreign Agents Registration Act (FARA) governing foreign lobbying and influence, and Fusion GPS' ties to a legal case involving the Magnitsky Act, a law intended to punish human rights violators in the Kremlin. In doing so, Grassley poked at the credibility of accusations of any ties between Mr. Trump and Russia.

"Mr. Simpson's company, Fusion GPS, is the same firm that oversaw the creation of the unverified Russian dossier," Grassley said in the hearing. "Around the same time, Fusion also helped orchestrate a campaign to repeal the Magnitsky Act, for the benefit of Russian governments. There are public reports that the FBI used the dossier to kickstart its Russian investigation. Did the FBI know that Fusion pitched propaganda for the Russians, even as it pushed the dossier? What would they say about its reliability if the dossier was represented to any court, should this fact have been disclosed?"

With the Senate Intelligence Committee investigating Russian election meddling and any connections between Mr. Trump's campaign and Russia, Grassley has turned to investigating related matters. The Republican is also investigating how Russian lawyer Natalia Veselnitskaya, who met with Manafort, Trump Jr. and Mr. Trump's son-in-law Jared Kushner at Trump Tower in June 2016, was allowed to be in the U.S. in the first place.

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In a continuation of Wednesday's hearing on Thursday, William Browder, who heads up Hermitage Capital Management, is expected to accuse Fusion GPS, Veselnitskaya and American lobbyist Rinat Akhmetshin of trying to smear Sergei Magnitsky, who died in a Russian prison in 2009 after revealing a $230 million tax theft. The Magnitsky Act is named after him. Browder will argue that if Fusion GPS lobbied on behalf of the Russian government without registering with the U.S. government, it would violate FARA.

"Veselnitskaya, through Baker Hostetler, hired Glenn Simpson of the firm Fusion GPS to conduct a smear campaign against me and Sergei Magnitsky in advance of congressional hearings on the Global Magnitsky Act," Browder's prepared testimony reads. "He contacted a number of major newspapers and other publications to spread false information that Sergei Magnitsky was not murdered, was not a whistle-blower and was instead a criminal. They also spread false information that my presentations to lawmakers around the world were untrue."

Sen. Dianne Feinstein (D-California), the ranking member on the committee, said it's time to put teeth into FARA:

"I don't know a time when the United States feels more invaded, and by this I mean, 21 states' election systems were pierced in this last election, we believe by Russia," Feinstein said, calling that, an "interference with our sovereignty."