In a Friday letter to the DOJ’s Inspector General Michael Horowitz, Grassley and Issa said they’re now concerned retaliation is much more likely following Thursday’s votes to hold Attorney General Eric Holder in criminal and civil contempt of Congress.

“We just learned that ATF senior management placed two of the main whistleblowers who have testified before Congress about Fast and Furious under the supervision of someone who vowed to retaliate against them,” they wrote before describing how senior political figures have made dangerous threats before.

Grassley and Issa said that in early 2011, right around the time Grassley first made public the whistleblowers’ allegations about Fast and Furious, Scot Thomasson – then the chief of the ATF’s Public Affairs Division – said, according to an eyewitness account: “We need to get whatever dirt we can on these guys [the whistleblowers] and take them down.”