The latest revelation comes in a report Thursday in the Los Angeles Times, which says Heffelfinger may have been placed on a list of U.S. attorneys to be fired because his office was working to protect the voting rights of off-reservation Indians in Minnesota.
The Times reported that former Bush Justice Department appointee Bradley Schlozman put an end to Heffelfinger's inquiry into concerns that Native Americans were not going to be allowed to use tribal identification cards when voting off of reservations.
"This is a long and complicated legal story, but the real issue is this -- there is now evidence that the decision to put Tom Heffelfinger on this list may well have been politically motivated, that it may well have been due to an actual ongoing investigation in a case," said Klobuchar.
Heffelfinger ended up leaving his post voluntarily.
The latest revelation comes a week after another key Justice Department official confirmed that Heffelfinger was on the department's list of 30 U.S. attorneys for replacement, if he had not resigned on his own.
Monica Goodling testified before Congress that Justice Department officials were concerned Heffelfinger was spending too much time on issues related to American Indians, although she was not specific about what exactly those issues were.
The Senate Judiciary Committee is scheduled to question Schlozman in a hearing next week.