Rep. Mac Thornberry is the latest Texas Republican to head for the exits, announcing Monday that he is not running for reelection. The 13-term lawmaker is the top Republican on the House Armed Services Committee.

Thornberry was facing GOP term limits on the committee, having served two previous terms as chairman before the start of the current Congress, where he became the ranking member after Democrats took over the House.

“We are reminded, however, that ‘for everything there is a season,’ and I believe that the time has come for a change,” Thornberry said in a statement. “Therefore, I will not be a candidate for reelection in the 2020 election.”

Thornberry is the sixth of the 23 Texas Republicans serving in the House to decide to retire rather than run again in 2020.

A staunch defense hawk, Thornberry was a reliable — and effective — advocate for higher defense budgets. During his time as HASC chairman, Thornberry successfully shepherded significant budget increases (spending grew to $700 billion in 2017 and $716 billion in 2018) for the Pentagon through a highly divided Congress.

But as ranking member of the committee, Thornberry understandably saw his leverage decrease. During the fiscal 2020 National Defense Authorization Act markup, Thornberry pushed for a $750 billion topline, leading his caucus in voting against the bill in committee in protest when Democrats stuck to $733 billion.

Later, a two-year budget deal struck by leadership of both parties set the 2020 national security topline at $738 billion, $12 billion lower than Thornberry’s “must-have” number.

During his time in HASC leadership, Thornberry remained laser focused on securing funding for the Pentagon, often staying out of the political frays that stemmed from new policy positions staked out by the Trump administration.

He largely avoided staking out controversial positions on Iran, North Korea, and Syria, even when then-Defense Secretary James Mattis resigned in protest over Trump’s plan to reduce troop levels in the latter country.

Thornberry supported the president’s position on border security, but not the raiding of Pentagon accounts to funding using money that had been appropriated for military construction projects. But even when he disagreed with the president, he stopped short of openly criticizing Trump.

The 13th District he represents, which is in the northern part of the state and includes Armarillo, is not expected to be competitive in 2020. President Donald Trump carried the district by 64 points in 2016 and Thornberry won reelection in 2018 by 65 points. Inside Elections with Nathan L. Gonzales rates the 13th District race Solid Republican.

Thornberry was first elected to Congress in 1994 but he wasn’t new to politics. He had previously served as chief of staff to two Texas Republican House members and was deputy assistant secretary of State for legislative affairs for President Ronald Reagan.

Thornberry’s decision may be influenced by his committee prospects if he were to serve another term. He served as chairman of the Armed Services Committee when Republicans controlled the House and he’s currently the ranking member on the panel.

In 2021, he’d run into the GOP’s self-imposed term limit for committee leaders. Adopted in adopted in 1994, the rule specifies that a Republican House member cannot lead a committee for more than six years unless they obtain a waiver from the Republican Steering Committee. Time served as chair and ranking member both count toward the six-year limit.

The idea of changing the rule, including possibly not counting years in the minority against the limit, has been discussed in the conference. President Donald Trump took aim at the rule, saying it was driving the growing list of Republican retirements.

“House Republicans should allow Chairs of Committees to remain for longer than 6 years,” Trump tweeted earlier this month. “The Dems have unlimited terms. While that has its own problems, it is a better way to go. Fewer people, in the end, will leave!”

Katherine Tully-McManus contributed to this report.