Texas House Speaker Joe Straus, a San Antonio Republican, announced Wednesday he will not run for re-election in 2018, a decision that has the potential to upend the political balance of power of the state.

Straus, who has lately been the most powerful moderate Republican in the Texas Capitol, said he will serve until the end of his term. But that means there will be a new speaker when the Legislature next convenes in 2019.

His decision will immediately set in motion a scrum for control of the House, pitting arch-conservative members who have opposed him against the more centrist Republicans who have backed Straus.

Straus has clashed with hardline conservatives in recent years, not least Republican Lt. Gov. Dan Patrick. Tea Party leaders and their allies have blamed Straus for killing controversial measures backed by the hard right, most notably a  bill that would have regulated which bathrooms transgender Texans could use.

"I believe that in a representative democracy, those who serve in public office should do so for a time, not for a lifetime. And so I want you to know that my family and I have decided that I will not run for re-election next year," Straus said in a campaign email. "My time as a State Representative and as Speaker will end at the conclusion of my current term."

The announcement prompted gloating by Straus' critics and regret from his allies. Rep. Matt Schaefer,  R-Tyler, who clashed with Straus as chairman of the House Freedom Caucus, tweeted, "It's morning in Texas again!" Straus ally Rep. Charlie Geren, R-Fort Worth, said "I'm disappointed but I respect his decision."

Minutes after the announcement, one of Straus' top lieutenants revealed that he also won't be returning to the Capitol. Rep. Byron Cook, R-Corsicana, who is chairman of the House State Affairs Committee, said in a statement first reported by Quorum Report that he "will pursue other opportunities to serve our great state."

If Straus had remained in office and won the speakership, it would have been a record-breaking sixth term as leader of the chamber. First elected to his district in 2005 in a special election, Straus has been speaker since 2009.

In his statement Straus acknowledged his decision was “unexpected.”

“It’s been decades since someone has left the Speaker’s office on his own terms. But we have accomplished what I hoped the House would accomplish when I first entered this office, and I am increasingly eager to contribute to our state in new and different ways.”

No longer serving as speaker would allow a “greater opportunity to express my own views and priorities,” Straus said, adding that he would “continue to work for a Republican Party that tries to bring Texans together instead of pulling us apart.”

As speaker, Straus increasingly clashed with conservative elements within the GOP over issues like private school vouchers and the “bathroom bill” championed by Patrick. He was also openly critical of Gov. Greg Abbott’s agenda for the July special session, comparing it to a to "a room full of horse manure."

“Our party should be dynamic and forward-thinking, and it should appeal to our diverse population with an optimistic vision that embraces the future,” Straus said in the campaign email. “I plan to be a voice for Texans who want a more constructive and unifying approach to our challenges, from the White House on down.”