After hearing about the phone call between US President Donald Trump and his Ukrainian counterpart, Elaine Luria felt she no longer had a choice.

Key points: Congresswoman Elaine Luria supports impeachment hearings against Mr Trump

Congresswoman Elaine Luria supports impeachment hearings against Mr Trump She is in a marginal Virginia seat and could lose in 2020

She is in a marginal Virginia seat and could lose in 2020 Ms Luria said she felt like she had a patriotic duty to act

The Democratic Congresswoman had resisted her colleagues' calls to impeach the President for months.

She feared Robert Mueller's report into Russian election meddling would be too convoluted for voters to understand and she was not convinced the Commander-in-Chief had committed an offence that warranted early removal from office.

But Mr Trump's now-infamous conversation with Ukraine's President Volodymyr Zelensky changed everything.

Suddenly the Congresswoman felt she had a patriotic "duty" to act.

"It is clear the President of the United States abused his office," Ms Luria said.

"He asked a foreign country to dig up dirt on a political rival for his own personal political gain and used military aid for leverage."

Ever since he was elected, the impeachment of Mr Trump has seemed a possibility in Washington.

Ms Luria played a small, yet important role, in helping make it now a near certainty.

In September, the 20-year Navy veteran wrote a Washington Post opinion piece with six other first-term Democrats calling for an inquiry to begin.

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They all had lengthy national security backgrounds, they had all won their districts from a Republican at last year's midterms, and they are all considered vulnerable at the 2020 election.

Their support for impeachment seemed something of a tipping point.

After the opinion piece was published, many other Democrats also spoke out in favour, and Speaker Nancy Pelosi formally launched the investigation a day later.

"What Donald Trump has done is so clear cut and such a threat to our national security," Ms Luria said.

"He tried to leverage foreign involvement to boost his re-election campaign."

But now Ms Luria is facing some outraged constituents, Republican-funded attack ads, and the possibility of losing her job after just two years.

Democrats and Republicans draw impeachment battlelines

The Democrats are trying to keep their impeachment investigation simple.

The case centres around an anonymous CIA whistleblower complaint about a July phone conversation between Mr Trump and Mr Zelensky.

The Commander-in-Chief used the chat to ask for a "favour".

He then urged the newly elected Mr Zelensky to investigate unsubstantiated corruption allegations against former US vice-president Joe Biden and his son Hunter.

The latest written and oral testimony shows American diplomats understood, and were worried, that about $570 million in US military aid was conditional on the politically motivated Biden inquiry being launched.

"I believe that it's an impeachable offence … it's a textbook offence," constitutional law professor Susan Low Bloch said.

She testified during Bill Clinton's impeachment proceedings in 1998, the only woman on a panel of experts to do so.

Law Professor Susan Low Bloch believes Donald Trump committed a textbook, impeachable offence. ( ABC News: Niall Lenihan )

"I believe this is an abuse of office. The money was approved by Congress so it's not up to Trump to say, 'I won't give it to you unless you do me a favour and investigate one of my main political opponents.'"

But impeachment is always a political process and despite the steady drip-feed of damaging information, the outcome of these proceedings already seems to be a foregone conclusion.

The Democrats, who control the lower house of Congress, are expected to vote by the end of the year to make Donald Trump just the third US President ever impeached.

Then the case will move to the Senate for a trial as early as January, where the Commander-in-Chief's Republican colleagues have the numbers.

Currently, they look set to acquit him of all charges.

Corey Lewandowski insists Donald Trump's opponents are speaking out about him unfairly. ( ABC News: Niall Lenihan )

Former Trump campaign manager and current presidential confidant Corey Lewandowski is sure his former boss will make it through the process.

"This is just another attempt to overturn the 2016 election," Mr Lewandowski said.

"I also think this will cost the Democrats at the 2020 election, just like it cost the Republicans after they impeached [former president] Bill Clinton."

'I can't believe she's supporting this type of coup'

Surveys suggest the nation remains deeply split on the issue of impeachment.

According to the RealClearPolitics poll average, 48 per cent of Americans want Mr Trump impeached and removed from office, while 45 per cent are opposed.

Elaine Luria saw it as her "duty" to act, and is not concerned if her actions ultimately cost her her job. ( ABC News: Niall Lenihan )

Voters break largely along party lines. About 83 per cent of registered Democrats support the current push, compared to just 11 per cent of Republicans.

With the country so divided and the election less than 12 months away, both parties are already pumping money into justifying and selling their positions on impeachment.

In Ms Luria's marginal district, Republican attack advertisements have aimed to link the moderate Congresswoman with the left-wing of the Democratic party.

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She has hit back with a campaign ad of her own, trying to fundraise off the inquiry, but concedes a few of her constituents are disappointed with her.

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At a town hall meeting which the ABC attended, there was some noticeable tension.

"This is a Soviet-style type of trial, I can't believe she's supporting this type of coup," Trump supporter Judy Bono declared.

She repeatedly interrupted and heckled Ms Luria, while the Congresswoman was on stage trying to explain her position.

"Sixty-three million Americans voted for Donald Trump. They won't let the man do his job," Ms Bono added.

It is still unclear what the overall impact the impeachment investigation, a likely trial and then acquittal, will have on the 2020 election campaign.

But Ms Luria insists she does not care if it ends for her with electoral defeat.

"This is not about getting re-elected. This is about doing the right thing," she said.

"This is what's right for our country. I did not serve 20 years in uniform to watch our constitution be trampled on."