By early next year, this city best known for being the rodeo capital of Texas is on track to become a centerpiece of the American effort to increase artillery production vital to the war in Ukraine.

A hulking new plant going up next to a highway exchange not far from downtown Mesquite promises to nearly double current U.S. output, replenishing stockpiles and preparing more ammunition to beat back the Russian invasion.

For a city in the midst of engineering an economic renaissance, the General Dynamics Ordnance and Tactical Systems factory is a major boon. It is expected to employ a minimum of 125 people; bring business opportunities to local suppliers, retailers and restaurants; and, city officials hope, potentially help turn the area into an industrial hotbed of well-paying jobs.

None of that appears to have persuaded Representative Lance Gooden, the Republican whose district will house the new plant, to support continuing U.S. aid to Kyiv. Over the summer, he joined dozens of his G.O.P. House colleagues in calling for an end to American support for Ukraine’s fight, voting for measures to strip $300 million in security assistance for the war-torn country from next year’s defense budget and prohibit Congress from approving any more funds for the conflict.

His opposition and that of many others in his party has imperiled President Biden’s request for $24 billion in additional funding for the war, threatening to derail an emergency spending bill that lawmakers in both parties are working to push through Congress this month.

It reflects how the “America First” mentality popularized by former President Donald J. Trump has spread and intensified among Republicans, prompting increasing numbers of lawmakers — including some whose constituents benefit directly from continued American aid to Ukraine — to refuse to keep supporting it. And it is one major driver of the spending showdowns to come this fall as lawmakers toil to reach agreement on both the routine annual spending bills and an extra package of aid for crises at home and abroad.

Mr. Gooden’s office did not respond to repeated requests for comment. But opponents of the Ukrainian assistance programs have argued that the United States must disentangle itself from a faraway war and instead focus the government’s attention and money on problems closer to home.

Speaker Kevin McCarthy, who had said he backed continued funding for Ukraine, now appears to be bowing to the resistance on the right. He is considering dropping the aid for Kyiv and pushing through a $16 billion package of emergency disaster aid for states coupled with more money for border security.

The situation has dismayed some local business leaders in Mesquite, who — while taking pains not to criticize any politicians by name — say the opposition of some lawmakers to the funding measure is a slap in their constituents’ faces.

“I would love for them to talk about, ‘Hey, this will create manufacturing jobs in the U.S., this will create advanced manufacturing jobs in the U.S.,” Alexander Helgar, the president of the Mesquite Chamber of Commerce, said in an interview in his office. Lawmakers who oppose continued aid to Kyiv are effectively “voting against your constituents, at that point,” he said. “You’re literally saying no to the people you’re representing.”

The rush to arm Ukraine, combined with Kyiv’s seemingly insatiable need for weapons and ammunition, has prompted a defense production bonanza in the United States, as officials have scrambled to replenish inventories and build reserves better equipped to sustain Ukraine and respond to similar conflicts in the future.

Since Russia’s invasion, Congress has approved approximately $43 billion in security assistance for Ukraine, alongside other investments in the defense industrial base. The funds have injected new life, in the form of government contracts, into factories across the country, including Abrams tank production lines in Lima, Ohio; Javelin missile factories in Ocala, Fla., and Troy, Ala.; and a plant that makes the propulsion motors for guided multiple-launch rockets in Rocket Center, W.Va.

But while lawmakers representing those facilities have welcomed the windfall, they have voted to curtail the funding that made it possible.

“We’re proud that they’re made in Ohio’s Fourth District,” Representative Jim Jordan, the Republican whose district includes the Lima Army Tank Plant, said of the Abrams tanks, “but our constituents have great concerns about seemingly unlimited taxpayer money being used to fund the war in Ukraine, especially when Americans are struggling at home with rising inflation and places like East Palestine and Maui continue to be ignored by the Biden administration.”

Their stance breaks with decades of bipartisan support for feeding the military-industrial complex. Nowhere is that disconnect more apparent than in Mesquite. The city had no foothold in the defense industry before the Ukraine war created skyrocketing demand for 155-millimeter shells, the ammunition fired from howitzers, long-range weapons central to the artillery battles that have defined much of the conflict.

The U.S. government plans to expand 155-millimeter shell production from pre-Ukraine-war levels of less than 15,000 per month to 90,000 per month, and Mesquite’s plant is expected to contribute about 20,000 toward that goal once it comes online in early 2024.

The city invested over $1 million in land and water line costs to attract the General Dynamics plant, while the local power company built a new substation to meet its electrical needs. It was all part of an effort to attract higher-skilled production industries offering wages that would encourage residents of this fast-growing city to work and spend money in Mesquite, where despite a recent proliferation of housing developments and major corporations opening warehouse distribution hubs, empty storefronts still dot many blocks of the historic downtown.

“You do see small businesses benefit when these larger businesses come to the community,” said Kim Buttram, the director of economic development for the City of Mesquite. Advanced manufacturing companies like General Dynamics, she added, also “offer our citizens, our students, our folks, opportunities to up-skill and better their career opportunities close to home.”

To that end, the city has made a point of promoting vocational training programs through the public secondary schools and the local community college, to prove to similar companies that there is a ready work force waiting to be tapped. City officials hope the General Dynamics plant as well as a large Canadian Solar panel production facility and a truck and auto vehicle accessory plant that are expected to begin operations this year will be models for how advanced manufacturing firms can thrive in Mesquite, helping the community flourish in the process.

But much depends on what happens in Washington.

The Army has already announced that it plans to spend almost $1 billion on 155-millimeter artillery rounds over the next five years. But while the Army’s ordnance contracts are multiyear commitments, they are not permanent purchase orders — and their long-term durability depends on Congress’s continued willingness to fund production, even once the new stockpile quotas have been reached.

“All this is subject to appropriation, and it is not at all certain that this level of appropriation will continue for the whole time it would take to reach an inventory,” said Bradley Martin, the director of the National Security Supply Chain Institute at the RAND Corporation.

As Congress gets closer to a reckoning over continuing Ukraine funding, Republican supporters of the war have begun to point to places like Mesquite to bolster their argument for keeping the aid flowing.

“The money we’re talking about doesn’t go to Ukraine; it goes to defense manufacturing facilities all across America and supports tens of thousands of American jobs,” Senator Mitch McConnell of Kentucky, the minority leader, said on the floor last week. “Critics of this investment cannot ignore its returns. American industry and workers are stronger for it, our war fighters are stronger for it and our nation is stronger for it.”

Mesquite city officials, who are careful to sidestep politics when they discuss economic development projects, frame the sudden connection between their fortunes and those of the Ukrainians a bit more delicately.

“We don’t want to say we’re profiting off of a conflict like that — we’re not feeling any of the effects of war,” said Cliff Keheley, Mesquite’s city manager. “But at the same time, it’s a global scale of the economy, and that generates a need.”

“At the end of the day, somebody’s got to do these jobs,” Ms. Buttram added. “It might as well be us.”

John Ismay contributed reporting from Washington.