The NY Times offers this report. A snippet:

Mr. Graves said he had taken at least three stands on cases that may have alienated officials in Washington, adding, “I guess to them I wasn’t a team player or something.”
Two of those cases involved the civil rights division, which has been a focus of Congressional investigators because of accusations that it has become more partisan in the Bush administration, pushing Republican causes. In one case, Mr. Graves said, the civil rights division had wanted him to sue the State of Missouri for what federal officials thought was its failure to purge voter registration roles of people who had died, changed addresses or left the state.
Mr. Graves said he believed the suit would not succeed because local governments are responsible for registration records. After his refusal to sign off, the lawsuit was authorized by Bradley J. Schlozman, then the acting chief in the civil rights division in Washington. The department named Mr. Schlozman as Mr. Graves’s interim successor.
The administration saw such lawsuits as a way to combat voter fraud. But Democrats have said the lawsuits were politically motivated because poor and elderly voters were more likely to be taken off registration rolls.
The lawsuit was dismissed when a federal judge concluded that the state could not enforce the purging of local voter registration rolls.

See also this editorial. You can find my coverage of that Missouri NVRA lawsuit in an earlier post, Another DOJ Failure to Prove Voter Fraud.