EL PASO — Representative Will Hurd of Texas, the only black Republican in the House, announced Thursday that he would not seek re-election next year, adding to a wave of departures that has unsettled party leaders as they hope to reclaim the majority in 2020.
Mr. Hurd, who is also the only Republican to represent a district along the southwestern border, is the sixth House Republican and the third Texan in the past 10 days to announce retirement. After the 2020 election, Senator Tim Scott, Republican of South Carolina, will be the only black Republican incumbent in Congress.
“Two centuries ago, I would have been counted as three-fifths of a person, and today, I can say I’ve had the honor of serving three terms in Congress,” Mr. Hurd said Thursday in a statement. “I will keep fighting to remind people why I love America: that we are neither Republican nor Democrat nor independent.” He did not say what he planned to do next. Before serving in Congress, Mr. Hurd was an undercover C.I.A. officer.
His announcement on Thursday made clear that the Republicans’ path to reclaiming the majority in the House and diversifying their party’s membership was becoming increasingly difficult. Two of 13 female incumbents — Representatives Martha Roby of Alabama and Susan W. Brooks of Indiana, who is a leader in candidate recruitment — and a handful of moderates are not planning to run again.
In the past few days, Representatives K. Michael Conaway of Texas, Rob Bishop of Utah and Paul Mitchell of Michigan also announced their plans to retire, while Representative Rob Woodall of Georgia made his decision known in February.
Hours after Mr. Hurd’s announcement, David Wasserman, the House editor of the nonpartisan Cook Political Report, said the report’s prediction for Mr. Hurd’s district had been moved to “leaning Democrat” from “tossup.” The Texas district represented by Pete Olson, another Republican who recently announced his retirement, is also now rated as “tossup.”
Mr. Hurd, whose district sprawls from San Antonio to El Paso and is larger than some states, has held onto his seat by a winnowing margin, defeating his opponent, Gina Ortiz Jones, in 2018 by a little over 1,100 votes. He has overcome the geographical and electoral perils of Texas’ 23rd District by building a reputation as a dedicated legislator willing to work across the aisle, which made his decision even more devastating for state and national Republicans.
“It’s a huge loss for the district — it almost can’t be overstated,” said Matt Mackowiak, a Texas-based Republican consultant, adding, “He’s been running a marathon like a sprint for seven years.”
That often meant breaking with President Trump and the Republican Party. Mr. Hurd, who has voted just over half of the time for positions held by Mr. Trump, like building a wall along the southwestern border, instead speaks of a border guarded by fiber optic cables, sensors, radar, drones and increased staffing.
Mr. Hurd was also one of only a handful of Republicans to join Democrats last month in condemning Mr. Trump’s attacks on four freshman Democratic congresswomen of color. And he had also been growing more vocal about his frustration with the current direction of the party.
“The party is not growing in some of the largest parts of our country,” he said in a June speech to the Log Cabin Republicans, a conservative L.G.B.T. group. “Why is that? I’ll tell you.”
“Don’t be a racist,” Mr. Hurd went on to say, according to the The Washington Blade. “Don’t be a misogynist, right? Don’t be a homophobe. These are real basic things that we all should learn when we were in kindergarten.”
Representative Tom Emmer of Minnesota, the head of the House Republican campaign arm, on Thursday hailed Mr. Hurd’s “lifetime of service to our country” and vowed to “fight tooth and nail to ensure it remains in Republican hands in 2020.”
But Mr. Emmer’s Democratic counterparts, who have already singled out Texas as a 2020 target, voiced the same confidence. Avery Jaffe, a spokesman for the House Democratic campaign organization, said in a statement that “if Will Hurd doesn’t believe he can keep his job in a changing Texas, his colleagues must be having second thoughts, too.”
Ms. Ortiz Jones, who lost to Mr. Hurd in 2018 and has declared her intention to run in 2020, said in a statement that she respected Mr. Hurd’s “decision to serve in a new capacity” and vowed to fill his void.
Representative Veronica Escobar, Democrat of Texas, whose district in El Paso borders Mr. Hurd’s, said in a brief interview in El Paso that she hoped “now that he is no longer running for office, that he’s liberated and can speak truthfully about the danger of this lawless president.”
News of Mr. Hurd’s retirement resonated across both parties, with Representative Elise Stefanik, Republican of New York, calling him “a friend for life” and promising that “Americans will hear more from him in years to come.”
Representative Hakeem Jeffries of New York, the chairman of the House Democratic Caucus, said that it signaled “the departure of a member of Congress who was reasonable, thoughtful” and “there for the right reasons.”