WASHINGTON — Sen. Lamar Alexander, R-Tenn., announced Monday that he will not seek election to a fourth term.

The state's senior senator, Alexander has a solidly conservative voting record but is known in the halls of the Senate as a consensus-builder on policy. Under GOP term-limit rules, the next Congress, which begins in January, will be his last as chairman of the Senate's Health, Education, Labor and Pensions Committee.

"I have gotten up every day thinking that I could help make our state and country a little better, and gone to bed most nights thinking that I have," he said in a statement. "I will continue to serve with that same spirit during the remaining two years of my term."

His home state has a decidedly Republican cast, having favored Donald Trump 61 percent to 35 percent in the 2016 presidential election. Republican Marsha Blackburn defeated former Gov. Phil Bredesen, a highly touted Democratic recruit, for the state's other Senate seat, 55 percent to 44 percent.

Alexander, 78, a former governor of Tennessee, education secretary under President George H.W. Bush, and two-time contender for the Republican presidential nomination, was able to turn back a Tea Party primary challenge in his last re-election bid in 2014.

During that campaign, he touted his work across party lines, which included supporting a rewrite of immigration laws designed to enhance border security, re-fashion the guest-worker program and create a path to citizenship for undocumented immigrants.

In the current Congress, he spearheaded a bipartisan law aimed at combating the national opioid crisis.

"I often tell him he is the legislator of the decade because of the effective way he has worked across the aisle to pass legislation that directly affects the lives of so many throughout our state and around the country," Republican Bob Corker, Tennessee's junior senator, said in a statement.