The FBI had over 40 confidential human sources involved in Biden family criminal investigations. However, the FBI's Washington Field Office shut down subpoenas, search warrants, and investigations into the Bidens, according to documents obtained by Sen. Chuck Grassley. The revelations were laid out in a letter Grassley, R-Iowa, wrote to Attorney General Merrick Garland and FBI Director Christopher Wray late Tuesday night obtained by Fox News Digital. "Based on the information provided to my office over a period of years by multiple credible whistleblowers, there appears to be an effort within the Justice Department and FBI to shut down investigative activity relating to the Biden family," Grassley wrote in a letter to Attorney General Garland and FBI Director Wray. "Such decisions point to significant political bias infecting the decision-making of not only the Attorney General and FBI Director, but also line agents and prosecutors." He added: "Our Republic cannot survive such a political infection, and you have an obligation to this country to clear the air." Source: Fox News Digital via @BrookeSingman