Top members of the Senate Judiciary Committee are expanding their probe into Russia's election meddling, asking for details on the communications of two Trump campaign aides.



Sens. Chuck Grassley Charles (Chuck) Ernest GrassleyGardner signals support for taking up Supreme Court nominee this year Grassley, Ernst pledge to 'evaluate' Trump's Supreme Court nominee McConnell digs in on vow to fill Ginsburg's Supreme Court seat MORE (R-Iowa) and Dianne Feinstein Dianne Emiel FeinsteinBiden leads Trump by 12 points among Catholic voters: poll Names to watch as Trump picks Ginsburg replacement on Supreme Court McConnell says Trump nominee to replace Ginsburg will get Senate vote MORE (D-Calif.) — the chairman and ranking member of the committee, respectively — sent a letter to the Trump campaign asking for documents related to John Mashburn and Rick Dearborn.



"The Committee has determined that obtaining their responsive emails, or at least ensuring that adequate searches have been conducted that would cover these communications, is necessary for its investigative work," Grassley and Feinstein wrote.



They noted they are sending the request because they "believe information obtained in a recent Committee interview warrants expanding those searches to two additional custodians who were not included in the original effort, John Mashburn and Rick Dearborn."



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Mashburn, who currently serves as a deputy Cabinet secretary, worked as a policy director on the Trump campaign. Dearborn, who announced late last year that he was leaving the White House, also worked on the campaign and the transition team.The Senate committee has been looking into Russian interference in the 2016 election since last year.Feinstein and Grassley noted they sent a letter in July 2017 asking for documents. So far, they said, the campaign has "provided over 28,000 pages of responsive documents, as well as letters detailing the 21 campaign custodians whose emails were searched and the more than 300 search terms used."

Grassley, Feinstein and Sens. Sheldon Whitehouse Sheldon WhitehouseHillicon Valley: Murky TikTok deal raises questions about China's role | Twitter investigating automated image previews over apparent algorithmic bias | House approves bill making hacking federal voting systems a crime House approves legislation making hacking voting systems a federal crime LWCF modernization: Restoring the promise MORE (D-R.I.) and Lindsey Graham Lindsey Olin GrahamGraham: GOP will confirm Trump's Supreme Court nominee before the election Fox's Napolitano: Supreme Court confirmation hearings will be 'World War III of political battles' Grassley, Ernst pledge to 'evaluate' Trump's Supreme Court nominee MORE (R-S.C.) sent letters last year to the Trump campaign, the Trump Organization and Donald Trump Jr. Don John Trump'Tiger King' star Joe Exotic requests pardon from Trump: 'Be my hero please' Zaid Jilani discusses Trump's move to cancel racial sensitivity training at federal agencies Trump International Hotel in Vancouver closes permanently MORE, President Trump Donald John TrumpBubba Wallace to be driver of Michael Jordan, Denny Hamlin NASCAR team Graham: GOP will confirm Trump's Supreme Court nominee before the election Southwest Airlines, unions call for six-month extension of government aid MORE's eldest son, asking for a slew of information about potential contacts with Russian officials, attempts to obtain damaging information on Democratic candidate Hillary Clinton Hillary Diane Rodham ClintonJoe Biden looks to expand election battleground into Trump country Biden leads Trump by 12 points among Catholic voters: poll The Hill's Campaign Report: Biden goes on offense MORE and a 2016 Trump Tower meeting with a Russian lawyer offering information on Clinton.

Thursday's joint Grassley-Feinstein letter comes as the Judiciary Committee's probe into Russia's election meddling has grown increasingly fractured in recent months.

Republicans, meanwhile, are digging into actions under the Obama administration, including the FBI's handing of its Russia probe and a separate investigation on Clinton's private email server.