Chief Justice John Roberts was asked to investigate ties between Justice Clarence Thomas and a wealthy Republican donor Harlan Crow|Chairman of the Joint Chiefs of Staff|CC BY 2.0

John Roberts, the US supreme court chief justice, has declined to testify at a forthcoming hearing before the Senate judiciary committee focusing on judicial ethics.

Roberts said such appearances by chief justices were exceedingly rare given concerns about the separation of powers between the branches of the US government and the “importance of preserving judicial independence”.

Harlan Crow scandal
He was invited by the committee’s Democratic chairman, Dick Durbin, who had earlier asked Roberts to investigate ties between Justice Clarence Thomas and a wealthy Republican donor.

Thomas, the longest-serving of nine justices, has been under pressure after reports by ProPublica detailing his relationship with billionaire Dallas businessman Harlan Crow.