Updated at 2:30 p.m.: Revised to include additional context and reaction.

WASHINGTON — The Texodus continues.

Rep. Mac Thornberry of Clarendon on Monday announced that he will not run for reelection next year, making the 13-term Panhandle lawmaker the sixth Texas Republican in Congress to head for the exits ahead of the 2020 election.

"We are reminded ... that 'for everything there is a season,' and I believe that the time has come for a change," he said in a news release, quoting a verse from Ecclesiastes. "Therefore, I will not be a candidate for reelection in the 2020 election."

"It has been a great honor to serve the people of the 13th District of Texas as their congressman for the last 25 years. They have given me opportunities to serve the nation in ways I could have never imagined, including as Chairman of the House Armed Services Committee. (1/2) — Mac Thornberry Press (@MacTXPress) September 30, 2019

His retirement marks a heavyweight loss for a state delegation in flux.

The congressman, elected to the U.S. House in 1994, is one of the longest-tenured Texans in Washington from either party. He's spent the last three terms as the top Republican on the powerful House Armed Services Committee, serving as chairman for two of those terms.

Of the 25 Texas Republicans who were House members in 2016 when President Donald Trump was sworn into office, only 11 are now slated to still be in Congress after next year.

While some of those departures point to Texas' emergence as a battleground state, Thornberry's decision does not. His district, which stretches from the New Mexico border to the outskirts of Fort Worth, is one of the most Republican in America and is all but certain to stay in GOP hands.

"R+33," said Bob Salera, a spokesman for the National Republican Congressional Committee, referring to GOP's massive advantage in a district that Trump won in 2016 with 80% of the vote.

But Thornberry's pending retirement underscores other dynamics.

The lawmaker is term-limited by GOP rules as the top Republican on the Armed Services Committee, meaning his influence was set to wane. His party faces stiff headwinds in winning back the House next year. An already-gridlocked Congress is bracing for a bruising fight over Trump's potential impeachment.

And no matter the motivating factor, Democrats celebrated the Texas GOP’s ongoing parade of exits.

"While we steadily invest in the Lone Star State, Washington Republicans just flew into Texas to declare they'll win back the majority and jetted away without a plan to stop the Texodus," said Lucinda Guinn, executive director of the Democratic Congressional Campaign Committee.

Added Manny Garcia, the Texas Democratic Party's executive director: "Thornberry retired because he didn't want to continue to serve in the minority."

The Texas GOP's retirement rush began in July, courtesy of Sugar Land Rep. Pete Olson.

Then came Midland Rep. Mike Conaway, the top GOPer on the House Agriculture Committee, another former committee boss. Then San Antonio Rep. Will Hurd, who represents a swing border district. Then Coppell Rep. Kenny Marchant, a vulnerable North Texas GOPer. Then Bryan Rep. Bill Flores.

Their departures follow an election cycle that saw six other Texas Republicans retire from Congress in 2018 — and two more lose their reelection bids.

"We're losing good people with great experience," said Texas Sen. John Cornyn, a Republican who's running for reelection next year. "But there are always some new people willing to serve."

Republican Party of Texas chairman James Dickey said he already planned to work to find a "qualified, conservative candidate" to replace Thornberry — whom he praised for his "aptitude and a constituent-driven focus" — and to "fight to keep Texas red in 2020 and beyond."

Limited clout

But the GOP drain comes as the party last year also lost control of the House for the first time in eight years. Most handicappers predict that Republicans will have a hard time winning back the chamber in 2020, and Texas Democrats are bullish about picking off more GOP seats.

That means congressional Republicans could be in the minority for the foreseeable future, severely limiting their clout.

"The difference between being a chairman and being a ranking member is like coaching the Dallas Cowboys versus coaching the Ennis Junior High School football team," former GOP Rep. Joe Barton, who retired last year, explained recently.

One additional factor in some of those retirements is the House GOP's policy on how long a lawmaker can hold the top spot on a committee. Unlike House Democrats, Republicans in that chamber limit those committee leadership posts to three two-year terms.

Conaway, the exiting Midland Republican, cited the term limits as a consideration. Other retiring Texans to face that restriction in recent years were Dallas Rep. Jeb Hensarling, who led the House financial services committee, and San Antonio Rep. Lamar Smith, who led the House science panel.

The trend appears to have the attention of House GOP leadership, which is now contemplating whether to allow members to serve longer in the top job, according to Politico.

But whatever policy change might be forthcoming apparently wasn't enough to sway Thornberry, who is a rancher and lawyer who worked as a congressional aide and State Department liaison to Congress at the end of the Reagan administration.

The Texan said on Monday that it was a "great honor" to represent his district.

"I could not have asked for a better group of employers than the people of the 13th District," he said. "Their faith, common sense and work ethic, along with a deep patriotism and devotion to our country, have encouraged and motivated me to do my best on their behalf."

Military focus

The Texan's time in Congress will be most remembered for his keen focus on military issues.

Thornberry's standing on the House Armed Services committee allowed him to be a powerful advocate for Texas' vast network of military installations. He also long pushed for increased defense spending, demanding that the military not suffer from congressional gridlock.

"Mac Thornberry is one the most substantive, decent people in Congress," said Brendan Buck, a former spokesman for former House Speaker Paul Ryan, a Republican. "A normal smart human being. In many ways he's the antithesis of what politics has become these days."

House Armed Services Committee Chairman Rep. Adam Smith, D-Wash., called Thornberry's retirement a "loss for the Congress."

"I have known Mac since I first came to Congress in 1997 and have always been impressed by his intelligence and tenacity," he said in a news release. "I am glad to have counted him as a colleague and will always call him a friend."

Though Thornberry's voting record shows stalwart support for Trump, the Texan did push back a few times against the commander in chief's policy ideas.

Some of that tension came over Trump's efforts to build a wall along the U.S.-Mexico border. While Thornberry supports the border wall itself, he's balked at using the military to build the barrier or tapping defense spending to fund the project.

"In short, I'm opposed to using defense dollars for non-defense purposes," he said in January, according to The Hill.

Staff writer Nic Garcia in Dallas contributed to this report.