Nine Republican leaders from across Pennsylvania on Wednesday endorsed Democrat Josh Shapiro for governor over their own party’s nominee, state Sen. Doug Mastriano, saying he is an extreme candidate who would undermine democracy.

Mastriano's relationship with establishment Republicans was already strained despite winning the May 17 primary against eight other candidates, a race that saw a groundswell of opposition from GOP leadership concerned that his far-right positions would drive moderate voters to Shapiro in November.

Mastriano has long been a supporter of unproven claims of voter fraud in the 2020 election. As chair of the Senate Majority Policy Committee, he held a hearing in Gettysburg that November that saw Rudy Giuliani, poll watchers and a phone call from former President Donald Trump espousing claims of irregularities in the election. Mastriano has also championed legislation to restrict abortion access in Pennsylvania, often without exceptions in cases of rape or incest.

“I have proudly voted for the Republican candidate for Governor throughout my life, but I cannot vote for someone as extreme and dangerous as Doug Mastriano,” said former state Supreme Court Justice Sandra Schultz Newman Greenwood, who represented the state’s 8th District between 1993 and 2005.

“Mastriano continues to fan the flames of division, doubling down on his threats to undermine our democracy and attacking anyone who dares to criticize him.”

The endorsement of Shapiro by Republicans is the latest sign of discord with Pennsylvania's GOP.