The route to passing Joe Biden’s $2.3tn infrastructure package runs through West Virginia.

The Appalachian state ranks 38th in population, 49th in median household income and second in coal production in the US. It has two senators like any other state, but the Democratic and Republican pair hold outsized influence over the president’s proposed spending plan.

West Virginia’s Joe Manchin, the most conservative Democrat in the Senate, has emerged as a pivotal dealmaker at a time when his party control the chamber by the slimmest of margins. He has made clear to the president that he expects the infrastructure package, called the American Jobs Plan, to pass with votes from both Democrats and Republicans.

In doing so he has shone a spotlight on his Republican counterpart Shelley Moore Capito, the junior senator from West Virginia, who has become the chief negotiator for Republicans in the infrastructure talks. She is among the handful of Republican senators who has been invited to meet Biden on Thursday at the White House to discuss infrastructure proposals.

West Virginia would benefit from the spending. Long one of the poorest states, its roads and bridges need repair. The American Society of Civil Engineers last year gave the state’s infrastructure a “D” rating, defined as “poor” or “at risk”, saying that much of it had deteriorated. One in five bridges are structurally deficient compared to the national average of 7 per cent, according to the society.

“When you look at the infrastructure problems across the United States, West Virginia is a pretty good example of what needs to be fixed,” said John Kilwein, a political-science professor at West Virginia University.

West Virginia was represented in the Senate for half a century by Robert Byrd, who was famed for delivering federal dollars to his state as chair of the appropriations committee.

“There is a historical legacy, given how adept Robert Byrd was at bringing pork to the state,” Kilwein said. “One person’s pork is another person’s important infrastructure. He really did bring money back to the state, and he did build infrastructure.”

Biden’s ambitious plans include ploughing an unprecedented amount of federal money into the nation’s roads, bridges, transport hubs, water facilities and broadband networks.

Republicans insist that while more spending is needed to repair crumbling infrastructure, any plan needs to be pared back, especially after the trillions of federal dollars allocated earlier this year for Covid relief. They have also bristled at the president’s proposals to raise the corporate tax rate or increase taxes on America’s top earners to pay for the extra spending.

As the senior-most Republican on the Senate environment and public works committee, Capito has taken the reins on drafting and making the case for a GOP counterproposal to Biden’s plan. Last month, she published a $568bn proposal heavily weighted towards traditional infrastructure projects, including $299bn for roads and bridges, $65bn for broadband, $61bn for public transit systems and $44bn for airports.

The daughter of West Virginia’s three-time Republican governor, Arch Moore Jr, Capito worked as a college counsellor before joining the state legislature and later winning election to the US House of Representatives in 2000.

Her largely rural state, where voters are mostly white and do not have college degrees, has swung sharply to the right in recent years, in part as a reaction to the decline of the state’s once-strong coal mining industry. West Virginia had the largest share of Trump voters of any state in the nation last November, bar Wyoming.

When Capito ran for the Senate in 2014 she took a sizeable 62 per cent of the vote and became the first woman to represent West Virginia. Last year she was re-elected with the backing of more than 70 per cent of the electorate as she shared a ticket with Donald Trump, who carried her state by nearly 40 points over Biden in November’s election.

Capito was ranked the sixth-most bipartisan senator out of 100 in an annual index compiled by the Lugar Center and Georgetown University’s McCourt School of Public Policy that tracks the degree to which senators work across political party lines on legislation.

Biden sat down at the White House with Manchin earlier this week. Capito told reporters on Capitol Hill she expected a “substantive meeting” on Thursday focused on finding common ground between the White House and the GOP offerings.

“When you narrow the focus as to what we consider infrastructure . . . if you eliminate some of the things that we don’t have in our plan, it closes the gap significantly,” she said, adding she was “very encouraged” by the communications she and other Republicans have had with the White House.

Mitch McConnell, the Senate’s top Republican, said at the weekend that he thought an infrastructure package should cost between $600bn and $800bn — indicating the GOP may be willing to edge higher than Capito’s initial proposal. After he met Biden on Wednesday he said that he would allow Republican committee leaders to work on a package with their counterparts, rather than pursue top-down negotiations.

Kilwein said Capito had a “tough tightrope to walk” to deliver for West Virginia voters while at the same time satisfying the demands of fellow Republicans.

But analysts said that it made sense for Capito and Manchin to take a central role in haggling over a nationwide infrastructure bill, particularly given the senators’ records of bipartisanship — and the grave need for improvements in the state.