Longtime Texas Rep. Mac Thornberry, House Republican’s top voice on military and national security issues, announced he will not run for re-election next year, ending his 25-year congressional career.

Thornberry, 61, serves as the House Armed Services Committee’s ranking member and was chairman of the powerful panel from 2015 to 2018. In a statement released Monday, he said he would finish out his current term and leave Congress in December 2020.

"With over a year to go, I will continue to represent the people of the 13th District to the best of my ability,” he said in a statement. “Our nation faces many difficult challenges, and none of us can relax our efforts to meet and overcome them, whether at home or around the world.”

Under House Republican rules, Thornberry was scheduled to step down from his post at the the top Republican on the Armed Services Committee at the end of this term. That has prompted speculation in recent months that the longtime defense advocate may retire.

Still, his departure leaves a significant void for the party in their national security messaging. Thornberry has been among the most vocal advocates of increased funding for the armed forces, arguing that cutbacks and slow growth has led to a decrease in readiness and in increase in mission risk.

At the same time, Thornberry has been focused in recent years on acquisition and operations reform at the Pentagon, arguing too much of the massive bureaucracy remains inefficient. Several of his proposals have been featured in the annual defense authorization bills passed in recent years, which he helped guide through Congress as committee chairman.

A number of Republican congressmen in recent months have announced their plans to leave elected office next year, including five others from Texas alone.

Thornberry did not reference any specific reason for leaving in his statement Monday, noting only that “I believe that the time has come for a change.” He added that he was proud to have been able to work on behalf of the military, “the pride of our nation as they serve us every day.”

The move is likely to set off a leadership scramble among defense Republicans in the House, given the power and public platform of the top Armed Services committee post.