AUSTIN, Tex. — Steve Mostyn, a Texas trial lawyer and one of the nation’s leading Democratic donors, who spent a fortune in a long effort to turn his reliably red home state blue, died on Wednesday at his home in Houston. He was 46.

The Harris County Institute of Forensic Sciences ruled the death a suicide resulting from a gunshot wound to the head. His wife and fellow lawyer, Amber Mostyn, said his death had come after a “sudden onset and battle with a mental health issue.”

The death jolted Texas politicians in both parties and left Democrats grieving the loss of a friend and wealthy patron who had been at the center of the party’s struggle to wrest power from Republicans. Texas Democrats have not won a statewide political office since 1994.

“Texas has lost one of its giants for justice and one of its most important voices for those without the ability or means to fight for themselves,” said Wendy Davis, a former Democratic state senator who ran for governor there in 2014, losing to Greg Abbott, a Republican and the current governor.