WASHINGTON — In his five years as chairman of the House Committee on Science, Space and Technology, Representative Lamar Smith transformed the once almost invisible position into a powerful bully pulpit. From it, he tried to dismantle Obama-era climate policies, undermine scientific consensus and browbeat federal agencies for what he called scientific fraud.

But with his run as chairman nearly done, the 69-year-old Texan announced on Thursday that he would retire rather than seek a 17th term in Congress and a spot on the backbench. The news followed closely on the heels of another powerful Texas Republican facing the end of his chairmanship, Representative Jeb Hensarling of the Financial Services Committee, who said just two days earlier that this term would be his last.

With a year left before the midterm elections, the line of senior House Republicans heading for the exits continues to grow. Democrats argue that the wave of retirements will help them retake the House.

But regardless of who controls the chamber come January 2019, it is becoming increasingly clear that the House will be a different place, with some of its biggest personalities and powerful committee and subcommittee leaders leaving it behind.