The move is unprecedented in Tennessee's modern political era. The last speaker resignation came in 1931 in the Senate.
"When I return to town on June 3, I will meet with caucus leadership to determine the best date for me to resign as speaker so that I can help facilitate a smooth transition," Glen Casada said in a statement.
The speaker announced the decision just a day after previously shrugging off a 45-24 secret ballot vote from his GOP caucus determining they no longer had confidence in his ability to lead the Tennessee House. Casada said he would work to regain his colleagues' trust.
Previously, he had spelled out an action plan designed to reassure fellow lawmakers and help him avoid having to step down.
But it wasn't enough for an increasing number of Republican leaders, including the House's top officers, who began demanding he step aside. They were joined by Republican Gov. Bill Lee, who warned that he would call a special legislative session if Casada didn't voluntarily resign.
The demands began earlier this month, when it was revealed that Casada had exchanged text messages containing sexually explicit language about women with his former chief of staff several years ago.
"Speaker Casada has made the right decision, and I look forward to working with the legislature to get back to conducting the people's business and focusing on the issues that matter most to our state," Lee, who was elected to his first term in November, said in a statement.
The resignation announcement marked a quick, turbulent downfall for Casada, who has spent only a few months in the House's top position.
The lawmaker from Franklin first stepped into the key role in January, eight years after he lost a bid for the position. In the November election, the then-majority leader received 47 out of 73 votes from Republicans in the 99-member chamber, defeating Reps. Curtis Johnson of Clarksville and David Hawk of Greeneville.
Casada built up political capital by spending heavily on Republican candidates in contests during the November election, including contested primaries for open Republican seats.
He began to lose that support when his former chief of staff, Cade Cothren, was pressured into resigning after the release of years-old racist texts and the sexually explicit messages, and Cothren's admission that he used cocaine in his legislative office years before becoming Casada's top aide. Casada was included in one of the group texts with a racist message, but has said he never saw it.
Another scandal that sparked early doubts was the report that Cothren may have tampered with evidence in a young black activist's criminal case, which a special prosecutor is still investigating.
Casada denied the tampering allegation and a variety of others that continued to pile up, ranging from accusations that he spied on legislative members to a GOP colleague's claim that Casada tried to "rig and predetermine" an ethics review regarding his controversies.
About a week ago, he addressed his fellow GOP House members about the texts and other issues, assuring them there was "nothing else to come out." It wasn't long until another text exchange emerged in a WTVF-TV report, in which he and Cothren - then the House Republican caucus press secretary - joked about the ages of two women and asked if they were 21 years old.
According to the texts, Cothren responded that "it only takes 18." Casada answered "Lol!!! And true!"
It's still unknown when Casada will meet with legislative leaders to determine his last day. Hours after he announced his resignation, Speaker Pro Tempore Bill Dunn told news outlets he was willing to serve as House speaker should the chamber elect him.
Separately, GOP Rep. Mike Carter, who originally raised concerns about the ethics investigation, told the Chattanooga Times Free Press he was asking staffers to prepare a petition calling for Casada's full removal from office.
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