Impeachment was contentious even when it was first proposed in the 18th century.

Allowing for the removal of a democratically elected president attracted some fierce opposition and wide disagreement on how high the bar should be set.

According to founding father Benjamin Franklin, impeachment existed for when the president "rendered himself obnoxious".

For James Madison it was "incapacity, negligence or perfidy".

The official purpose, as spelled out in the US Constitution, is to remove the president from office if he has committed "treason, bribery, or other high crimes and misdemeanours".

It is that second word, bribery, that House Democrats will likely use a lot in the foreseeable future.

They will say the account of this first phone call between President Donald Trump and Ukrainian President Volodymyr Zelenskiy goes part of the way to proving the President should be impeached.

And true to history's precedent, Republicans are offering a different take.

Both sides will be gearing up for a big fight. The conversation was hardly the 'perfect call' that the President said it was.

Trump explicitly uses the word 'favour'

The account of the call came in the form of a memo, released with permission from the White House. A note at the top says it is a "memorandum of the telephone conversation", based off notetakers' accounts and not necessarily verbatim.

The five pages of text begin with introductory congratulations and small talk, but it does not take long for Mr Trump to reference US military aid — he reportedly froze nearly $US400 million in funds the week before.

"I will say we do a lot for Ukraine," he says. "We spend a lot of effort and a lot of time. Much more than the European countries are doing."

Mr Zelenskiy brings up the aid again at a later point, saying that his country stands ready to purchase more US weapons.

Mr Trump's immediate reply?

He asks for 'a favour'.

"I would like you to do us a favour though because our country has been through a lot and Ukraine knows about it," the memo reads.

Mr Trump wants an investigation into the origins of the Mueller inquiry.

The two men then discuss Mr Trump's personal lawyer Rudy Giuliani visiting (he has no official government role and has been accused of spending months digging for dirt in Ukraine).

Ukraine's President Volodymyr Zelenskiy said he was ready to purchase more US weapons right before US President Donald Trump asked him for a "favour". ( Reuters: Chris Helgren )

Then comes the moment both political parties will be harping on.

"The other thing," Mr Trump says.

"There's a lot of talk about Biden's son, that Biden stopped the prosecution and a lot of people want to find out about that so whatever you can do with the Attorney-General would be great."

In the context of a conversation about restoring military aid, it turns out the President's full "favour" involves his chief political rival: former vice-president Joe Biden.

Trump pushed to reopen an old issue

Remember that Mr Biden is leading in the polls for the Democratic nomination and is currently considered the biggest threat to a second Trump administration.

Mr Trump also asks for the investigation to include Mr Biden's son Hunter Biden.

Hunter Biden is a troubled man. His public battles with substance abuse and a controversial relationship with his brother's widow have made him a regular conservative target for months.

The President makes it clear that he wants an old issue involving Hunter Biden to be reopened — the sacking of a prosecutor who was investigating a Ukrainian gas company whose board employed the younger Biden.

Mr Trump told the Ukranian President "our country has been through a lot and Ukraine knows about it". ( Reuters: Yana Paskova )

Complicated, right?

Investigators had previously found the US was pushing for the firing of this prosecutor because he was not prosecuting corruption enthusiastically enough, rather than it being an attempt by Biden Senior to protect his son.

But the prospect of a damaging inquiry involving a figure as tabloid-friendly as Hunter Biden appeared too good for Mr Trump to ignore.

A scandal with the drug-addicted son who received millions to work with a Ukrainian gas company would have filled hours on conservative US media outlets and could have damaged the Biden campaign.

The President promised his Attorney-General William Barr would call (the Justice Department says the President did not ask and the call did not happen).

Towards the end of the call, Mr Trump also promises an invitation to the White House.

Democrats will allege that is a further inducement.

It gives them plenty of grounds for their multiple inquiries.

Political reaction was swift and partisan

While there is legal grounding, impeachment is inherently political. This is again splintering on partisan lines.

Republicans say the President was right to raise potential corruption.

They also say it is sensible to withhold aid from countries where that is an issue.

Influential Republican senator Lindsey Graham robustly defended the President today.

"I read it just like you have," he told reporters. "You can make your own decision but from a quid pro quo aspect of the phone call, there's nothing there."

It is a sure sign his colleagues plan to hold the line. At least for now.

And that means removal from office probably is not going to happen.

Democrats could impeach Mr Trump in the House tomorrow. However, in the Senate, where he would face a trial overseen by the Supreme Court Chief Justice, Republicans hold the majority and all the power.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 36 seconds 36 s President Donald Trump has called the allegations against him as 'ridiculous' and a 'witch hunt'

At least 20 senate Republicans would need to vote with Democrats to reach the two-thirds majority to remove the President from office.

So far not a single one — even Republican Trump critics like senators Mitt Romney and Susan Collins — are on board with that.

Republicans will turn the spotlight on Joe Biden

Republicans will try and use this impeachment inquiry to continue their attacks on the Bidens.

Even if there is no fire behind the smoke they clearly view the troubled son as his father's Achilles heel.

You can also expect attacks on the candidate himself.

Once known as "middle class Joe," Mr Biden was one of the poorest senators. After a 30-year political career and time in the White House, Mr Biden has accumulated a multi-million-dollar fortune.

Mr Trump will point to his own storied wealth as proof he does not need to do these kinds of deals to be wealthy.

He will also point to the similarities with the failed attempt to oust Democratic president Bill Clinton through impeachment.

The economy was also strong during the Clinton trial, and voters harshly punished Republicans for trying to blast him out of office.

Democrats will invoke high-minded ideals

Democrats though are happy to have the fight on those terms, draping themselves in the flag and the founding fathers.

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They will make the case the very future of the union is at stake.

Be prepared to hear more from Benjamin Franklin, who once said:

"Those who can give up essential liberty to obtain a little temporary safety deserve neither liberty nor safety."

The battle lines for 2020 are being set. As they harden, any hopes of bipartisanship will vanish.