As the first televised hearing of the impeachment probe unfolded on Wednesday on the screen in his home in Flint, Michigan, Quincy Murphy said there was no chance the proceedings would alter his view that President Donald Trump is unfit to hold the office.

“I watch it in disgust,” said the 45-year-old autoworker, who voted for Democrat Hillary Clinton in 2016. “I haven't found anything to convince me that he is doing what's best for this country.”

More than 725 km away in his Bethlehem, Pennsylvania, barbershop, Trump backer Joe D'Ambrosio was equally adamant that the inquiry into whether the Republican president improperly pressured Ukraine to investigate a political rival would have no effect on his opinion.

“I fully support the president,” said D'Ambrosio, 76, as a mounted television showed the hearing live on Fox News. “I talk to a lot of people who are happy with their 401(k)s (retirement plans), their stocks and their jobs. Democrats don't want to talk about that, and I think they are going to pay a price.”

Democrats in the US House of Representatives hope a series of televised hearings will help persuade Americans that Trump deserves to be ousted from office.

But as the first day of the historic proceedings riveted Washington and dominated cable news, interviews with residents in two of the states likely to help decide the winner of next year's presidential election suggested voters on both sides had already made up their minds.

A November 4-5 Reuters/Ipsos poll showed that 75 per cent of Democrats supported impeachment, while 79 per cent of Republicans were opposed.

For many Trump supporters, the impeachment inquiry is nothing more than a partisan effort by Democrats to unseat a president they could not beat in 2016.

Trump is accused of holding up military aid to Ukraine, which has faced Russian aggression, unless the country's president agreed to announce investigations into Democratic presidential contender Joe Biden and the Ukraine business dealings of his son Hunter Biden. Trump has denied wrongdoing and calls the impeachment probe a sham.

“To me, it's a coup,” said retired construction worker Frank Buchualt, 70, as he sat in D'Ambrosio's barbershop. “I don't know what was illegal. We ask countries to do things all the time.”

But Murphy, who spends his nights assembling seats for the Chevrolet Silverado pickup truck, said the hearings offered Republicans a chance to prove they value the rule of law more than their own political survival. “The Republican Party is on trial,” he said.

‘Just a show’

In 2016, Trump flipped Pennsylvania, Michigan and Wisconsin, three states that for decades had voted Democratic in presidential elections, by less than 1 percentage point each, ensuring his victory in the Electoral College. The states are widely expected to be closely contested again in 2020.

John Cordisco, the Democratic chairman of Bucks County, a Philadelphia suburb that has historically served as a bellwether for the state and narrowly voted for Trump three years ago, said he doubted the hearings would have an impact given Trump's deeply polarizing presidency. He emphasised that members of Congress likely would have to cast votes on Trump's conduct, leaving them potentially vulnerable in their own elections next year.

Some voters expressed frustration that the lawmakers themselves appeared to have prejudged the case. “What I don’t appreciate is that many representatives and senators seem to have made up their minds already, before they've even seen the evidence and had a chance to discuss it in the appropriate setting,” Amy Hussar, a 42-year-old US Army retiree from Au Sable, Michigan, wrote in an email.

Hussar, a self-described moderate, voted for Democrat Barack Obama in 2008 and 2012 before casting a ballot for third-party candidate Gary Johnson in 2016, rather than for Clinton or Trump.

Even voters on the fence about Trump next year were unconvinced the impeachment proceeding would help them decide.“It's just a show,” said Kurt Zuhlke, a 64-year-old business owner in Northampton County, Pennsylvania, who voted for Trump in 2016 after supporting Obama and remains undecided for 2020.

“Everyone knows all the facts, and they have already made up their mind. This is not going to do anything.”