Charleston Gazette Mail via Associated Press, File, Tom Hindman
FILE - In this Thursday, Oct. 15, 2015, file photo, Don Blankenship, right, and his attorney Bill Taylor leave the Robert C. Byrd U.S. Courthouse in Charleston, W.Va. during a break. Blankenship is charged with conspiring to break mine safety laws and lying to financial regulators about safety at a West Virginia mine, which exploded in 2010, killing 29 men.

CHARLESTON, W.Va. — An outspoken critic of President Barack Obama charged with conspiring to violate mine safety rules before a deadly explosion is under orders not to tell jurors he's being persecuted by Democrats.

The federal judge also warned former Massey Energy CEO Don Blankenship that safety rules are not on trial.

But Blankenship hasn't checked his Republican politics at the courtroom door, and criticizing the inspectors remains key to his defense.

Blankenship's attorney William Taylor has argued that the U.S. Mine Safety and Health Administration inspectors targeted Massey's mines after Obama took office, spending twice as long in Upper Big Branch in 2009 as in 2007, under President George W. Bush.

He also said regulators demanded ventilation changes "almost impossible to implement" before an explosion killed 29 miners in 2010.