WASHINGTON — For months, Representative Darin LaHood appeared to be a sure Republican vote for President Biden’s major infrastructure bill that had passed the Senate with bipartisan support and was awaiting House consideration.

His Illinois district includes the heart of the nation’s heavy construction equipment manufacturing industry, where Caterpillar, Komatsu America and their suppliers are mainstays of the Peoria economy. The upstart electric truck maker Rivian in Normal, Ill., has much to gain from the bill’s funds to electrify the nation’s highways and boost its power grid.

His father, Ray LaHood, was a famously pro-infrastructure Republican member of the House who later served as President Barack Obama’s transportation secretary. And when the infrastructure bill was before the Senate this summer, the younger Mr. LaHood was an enthusiastic booster.

“I give the Biden administration and the bipartisan group of senators a lot of credit,” he told local reporters in July as he expressed optimism for a deal. “They keep working at this.”

Then last week, Mr. LaHood voted no, joining all but 13 of his fellow Republicans in opposition to the bill.

One of the 13 who voted for the measure was Representative Adam Kinzinger, who represents an Illinois district that adjoins Mr. LaHood’s.

The votes of both men say a lot about the Republican Party in an age of uncertainty. Former President Donald J. Trump is either vanquished or primed to return. House districts are being redrawn, deepening their partisan bent but adding hordes of new voters less acquainted with their representatives. Democrats face daunting odds of keeping their slim majorities in Congress and have spent months in disarray over Mr. Biden’s agenda, but they have just delivered one hugely consequential piece of legislation and appear on track to pass another.

In that atmosphere, Mr. LaHood appears to have put aside the clear economic interests of a district that will soon be radically reconfigured and stuck with his party’s line — and that of Mr. Trump — against the bill. The former president and his allies in the Republican leadership in Congress argued that the measure deserved to be defeated because Democrats were pushing a social policy and climate change “reconciliation” bill at the same time.

“I will continue to advocate for the transportation and infrastructure needs of my district, but I will not take part in helping the Democrats and Speaker Pelosi pass their irresponsible and partisan reconciliation package,” Mr. LaHood said in a statement explaining his vote. He declined to discuss it further.

Mr. LaHood is far from alone in his party. This week, as Senator Mitch McConnell of Kentucky, the Republican leader, promoted his vote for the infrastructure bill, he spoke hopefully about the crumbling Brent Spence Bridge linking his state to Ohio, which is likely to be replaced with funding provided by the measure. But Representative Steve Chabot, a Republican who represents the Ohio end of the bridge, voted against the legislation.

The New Harmony Toll Bridge, which links Illinois and Indiana over the Wabash River, has become something of a poster child for decrepit rural infrastructure since it was closed in 2012 over structural concerns. Representative Larry Bucshon, the Indiana Republican who represents New Harmony, voted no.

So did Representative John Moolenaar, a Michigan Republican whose district includes the Edenville and Sanford dams, which collapsed last year, forcing thousands to evacuate and inundating hundreds of homes and businesses.

Representative Joe Neguse, a Democrat who represents the eastern third of Colorado’s Eagle County, heralded the infrastructure bill this week as a lifeline for travelers over Vail Pass, a 10,666-foot crest on Interstate 70 that has some of the worst crash rates in the Rockies. Representative Lauren Boebert, the Republican who represents the western two-thirds of the county, voted no and, echoing Mr. Trump, blasted the 13 “RINOs” — Republicans in name only — who voted yes.

For Mr. Kinzinger, such insults were beside the point. Already an outspoken critic of Mr. Trump and House Republican leaders, he had announced his retirement days before casting his vote and is considering a run for governor in his Democratic-leaning state.

“This bipartisan package contains significant investments for roads, bridges, rails, seaports, airports and inland waterways — core infrastructure most Americans agree are in need of improvement,” he said in a statement. He could not be reached for comment because he was on military assignment for the Air National Guard.

The votes by Mr. Kinzinger and Mr. LaHood cannot be separated from the new House district map drawn by the state’s heavily Democratic legislature, nor can they be separated from Mr. Trump’s sudden interest in — and virulent opposition to — the bill.

The map crushed Mr. LaHood’s district and Mr. Kinzinger’s district together, potentially forcing the two incumbents to run against each other for the Republican nomination to represent Illinois’ new 16th District. The district still includes the suburbs of Peoria, where Caterpillar has long called the shots, and Greater Bloomington, home of Rivian, but it now stretches north to the Wisconsin border instead of west to the Iowa state line.

That gives the district huge swaths of rural territory that the bill targets for broadband access. The $6 billion in the bill to support struggling nuclear reactors could mean salvation for the Byron Generating Station outside Rockford, Ill., which Mr. Kinzinger has worked to keep operating. And the $2.5 billion in the measure for inland waterways could go a long way toward shoring up decrepit locks and dams on the Illinois River that are vital for efficiently transporting soybeans and corn from farms in the region to the Mississippi River.

But while the new 16th District may have infrastructure needs, it also has Republicans — lots of them — with a heavy conservative tilt. The new district will almost certainly be represented by the Republican Party in 2023.

Mr. Kinzinger saw the map and decided to retire rather than run against Mr. LaHood and go up against Mr. Trump, who had vowed to defeat him. Mr. LaHood saw a sea of new Republican voters to court and opted to side with his party’s leaders who were pressing rank-and-file members to reject the infrastructure bill. In doing so, they were hoping for an embarrassing defeat for Mr. Biden and Speaker Nancy Pelosi, even if it meant opposing infrastructure investment.

Mr. LaHood’s statement threw out red meat to the Republican base, savaging Senator Bernie Sanders, independent of Vermont, and “the radical progressive wing of the Democrat Party.” The statement warned of “an extreme reconciliation spending bill” waiting in the wings with “crippling tax hikes that will kill American jobs.”

Union members in his district said they were angry with his stance but not surprised by it. Randy Diehl, president of the United Automobile Workers Local 974 in Peoria, which represents about 3,300 workers, mainly at Caterpillar, and nearly 10,000 retirees, remembered Ray LaHood fondly, but he had nothing nice to say about his son Darin.

“He’s the worst of the worst, and for him to vote against infrastructure — for the 3,500 workers in the Peoria area, the 3,000 in Decatur, like 1,000 in Pontiac — it was a slap in the face,” Mr. Diehl said.

Sean Stott, director of governmental affairs for the Midwest region of the Laborers’ International Union of North America in Springfield, said the giant union had long supported Mr. LaHood but may reconsider.

“This was an enormously important issue for our members,” Mr. Stott said, adding, “It’s unfortunate that so many put partisanship above what’s best for the country.”

Still, it was Mr. Kinzinger whose office received a flood of angry phone calls, including one suggesting he take his own life, from people irate that he had dared to support the legislation.

For Mr. LaHood, the political price of voting against the bill seemed relatively lower at home, where many Republicans appeared to be giving him the benefit of the doubt.

Eli Nicolosi, the Republican chairman in Winnebago County, which includes Rockford, had the misimpression that the bill was full of social policies that had nothing to do with infrastructure, some of which are in the reconciliation bill. He said he understood and accepted Mr. LaHood’s vote, even though he noted that the local airport could use some help and that aerospace manufacturing would most likely benefit from a cash infusion.

Mike Dittmar, the chairman of the Jo Daviess County Republican Central Committee in Illinois’ northwest corner, also seemed unbothered by last week’s votes and said he did not even know that Mr. Trump had opposed the bill.

“I have not followed him since the election,” Mr. Dittmar said of the former president.

They did, however, seem ready to turn the page on Mr. Kinzinger, who has become a thorn in Mr. Trump’s side. A scorching critic of the former president’s leadership, Mr. Kinzinger voted for his second impeachment and is one of only two Republican members of the special House committee investigating the origins of the Jan. 6 attack on the Capitol by a pro-Trump mob.

“I definitely wish Mr. Kinzinger the best; he did a lot for us,” Mr. Nicolosi said, then added, “I can tell you right now, I think we’re all looking forward to a new start and getting a representative that we can all work with.”

Connie Beard, the chairwoman of the McLean County Republicans, brought up Rivian as a company of the future, but she worried aloud that the infrastructure measure would mean “tremendous amounts of tax increases.” Told that there were none in the bill, which is dominated by old-fashioned public works programs, Ms. Beard pivoted.

“It’s hard for the legislators themselves to understand what was left in the bill and what was on the cutting room floor,” she said, adding, “I understand why Congressman LaHood wanted to take more time.”