It will be the political fight of the century. Donald Trump is the first president since the 1990s to face impeachment by Congress. At best for him, it will be the dirtiest, most humiliating battle yet of a tumultuous political career. At worst, it will be the death blow to his presidency.

In a week for the history books, Trump was revealed to have used the powers of the Oval Office to solicit foreign interference in the 2020 election for his personal political interests – an abuse that the White House then tried to cover up.

Democrats moved swiftly to launch an impeachment inquiry following a whistleblower’s complaint that detailed how Trump pressed the leader of Ukraine to help smear a political rival, the former vice-president Joe Biden. It set the stage for weeks of partisan trench warfare likely to deepen national divisions. But it also offered a sliver of hope to Trump’s critics: that he could be drummed out of office by Christmas.

Nancy Pelosi, the House speaker, reportedly instructed congressional committees to keep a narrow focus on the Ukraine scandal rather than Trump’s myriad other alleged misdemeanours and to file the results of their investigations within weeks. With aides describing a “need for speed”, a vote to impeach could take place by mid-November.

“I think it’s going to happen fast,” said Elaine Kamarck, a senior fellow in the governance studies programme at the Brookings Institution in Washington. “The House is going to have to decide which articles of impeachment to draft and send forward. My guess is obstruction of justice and abuse of power.”

If the Democratic-led House votes to approve articles of impeachment, the Republican-controlled Senate will then decide whether to find Trump guilty and remove him from office. This seems far-fetched, but Kamarck said: “I’d give it a 30% to 40% chance. Remember how things shift and how public opinion shifts when you get these high-velocity events. There are people who’ve stood up to Trump in the Senate; they’re not totally terrified of him.

“We forget the human part: Trump has no friends. No one likes him. When push comes to shove, he doesn’t have depth and loyalty. If things get really bad and they can see a political future without him, they’ll abandon him.”

If there were a blind vote in the Senate, at least 30, possibly more of the Republican senators would vote to convict Michael Steele

To date, Republican senators have been cowed by Trump’s fervent support base and approval rating of around 90% within the party. But the relationship could prove fragile. A former Democrat, Trump was an outsider when he in effect staged a hostile takeover in the 2016 primary and many of his views are at odds with party orthodoxy.

Conviction requires a two-thirds vote of the 100-member Senate: 67 votes. That means 20 Republicans would be required to rebel. Michael Steele, former chairman of the Republican National Committee, said the challenge for Democrats was to win over public opinion.

“You know you’ve got the votes to impeach. The goal here is to create a narrative in which the American people wind up convincing the Senate they must convict.

“I know it’s true that if there were a blind vote in the Senate, at least 30, possibly more of the Republican senators would vote to convict the president. But they won’t do it absent a very public movement in that direction. In other words, the public itself, their base.”

Timeline of a scandal

Such comments are a measure of the gravity of Trump’s offence, different in kind from all those that went before. Unlike the special counsel Robert Mueller’s 448-page report on the Trump campaign’s contacts with Russia in the 2016 election and the president’s apparent attempts to obstruct justice, the attempt to extort Ukraine involved Trump personally, while in office, and can be summarised in no more words than a single tweet.

There was an early hint of trouble in May when the New York Times reported that Rudy Giuliani, Trump’s personal lawyer, planned to travel to Ukraine to press the government to investigate not only 2016 election interference but also claims Biden had pressured Ukraine to fire a prosecutor looking into a gas company where his son, Hunter Biden, was a board member.

Giuliani cancelled the trip, claiming the newly elected Ukrainian president Volodymyr Zelenskiy was “surrounded by enemies” of Trump. In June, Giuliani wrote on Twitter that Zelenskiy was “still silent on investigation of Ukrainian interference in 2016 and alleged Biden bribery”.

Trump, meanwhile, told ABC’s George Stephanopoulos he would consider receiving information on an election rival from a foreign source.

“I think you might want to listen, there isn’t anything wrong with listening,” he said. “If somebody called from a country, Norway, [and said] ‘We have information on your opponent’ – oh, I think I’d want to hear it.”

The following month, the president issued instructions to freeze nearly $400m approved by Congress to help Ukraine deal with an insurgency by Russian-backed separatists in the east of the country. On 24 July, Mueller testified to Congress but was widely seen as rambling and vague, failing to provide a smoking gun for impeachment.

A day later came Trump’s fateful phone call with Zelenskiy. After discussing military aid, he asked for a “favour” then later pressed the Ukrainian president to speak to Giuliani and the attorney general, William Barr, about reopening a Ukrainian investigation into Hunter Biden.

Trump said: “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. Biden went around bragging that he stopped the prosecution so if you can look into it … It sounds horrible to me.”

On 12 August, an intelligence community whistleblower filed a complaint. Another month passed. On 18 September, the Washington Post published the first details of the whistleblower complaint. It was very soon and very clearly a game changer.

This week, as political pressure built, the White House a released a rough transcript of Trump-Zelenskiy call. It showed the US president did indeed push his counterpart to dig up dirt on Biden. Critics called it extortion and “a classic mafia-like shakedown”. Pelosi announced an impeachment inquiry, citing the president’s “betrayal of his oath of office, betrayal of our national security and betrayal of the integrity of our elections”.

Volodymyr Zelenskiy listens during a bilateral meeting with Donald Trump in New York. Photograph: Jonathan Ernst/Reuters

On Wednesday, Trump and Zelenskiy met in person for the first time on the sidelines of the United Nations general assembly in New York. The Ukrainian leader, a political novice and former comedian, told reporters it was a “normal” call, insisting: “Nobody pushed me.”

But on Thursday the House intelligence committee released an unclassified version of the whistleblower complaint. The nine-page document said: “In the course of my official duties, I have received information from multiple US Government officials that the President of the United States is using the power of his office to solicit interference from a foreign country in the 2020 US election.

“This interference includes, among other things, pressuring a foreign country to investigate one of the President’s main domestic political rivals. The President’s personal lawyer, Mr Rudolph Giuliani, is a central figure in this effort. Attorney General Barr appears to be involved as well.”

It also alleged an attempt to conceal the offence, stating that White House officials took extraordinary steps to “lock down” information about the call, even moving the transcript to a secret computer system.

‘He loves fights’

The Zelinskiy phone call, and Trump’s willingness to make it public, renewed questions over his ability to distinguish right from wrong or understand the rule of law. Reaching for his familiar playbook, he made no apology and showed no contrition, but rather fired off a fusillade of tweets and retweets accusing Democrats of another witch-hunt.

And he jettisoned all norms in expressing special rage towards the whistleblower.

“I want to know who’s the person, who’s the person who gave the whistleblower the information, because that’s close to a spy,” Trump said to staff from the US mission to the UN. “You know what we used to do in the old days when we were smart? Right? The spies and treason, we used to handle it a little differently than we do now.”

He loves fights. That’s his comfort zone. He likes people being angry and yelling at each other Gwenda Blair

Gwenda Blair, a Trump biographer, said: “I don’t think right or wrong are categories he thinks in. The only category is, can he get away with it?”

Trump will be ready for the impeachment battle to come, Blair said. “He loves fights. That’s his comfort zone. He likes people being angry and yelling at each other. He gins that up any chance he gets. He did it at Trump Tower when he was running a real estate business.

“That combative atmosphere is what he thrives on. He’s comfortable when everyone else is uncomfortable, running and ducking for cover. That’s how he got elected, pitting people against each other. He’s into ‘bring it on’ because he’s in his element.”

The Republican and conservative media machines have cranked into gear. Giuliani has given a series of weird and wild interviews, insisting that he, not the whistleblower, was the true “hero” of the hour. Fox News hosts such as Sean Hannity expressed outrage at “psychotic anti-Trump hysteria” and demanded that Biden be investigated. There is no evidence of wrongdoing by Joe or Hunter Biden.

But Democrats who had long agonised over whether to exercise the ultimate sanction against a wayward president suddenly found bracing, galvanising clarity. Opinion polls show growing support for impeachment and Pelosi’s move has come as a relief to activists who felt that, having survived the Mueller report and countless other incidents unscathed, Trump felt unleashed and able to act with ever greater impunity.

Tom Steyer, founder of the Need to Impeach campaign and a candidate for the Democratic nomination for president, said: “I don’t think there’s any doubt that every time that Mr Trump got away with something it emboldened him to go further. I said from the beginning: it’s only gonna get worse if we don’t hold him to account.”

“Before this ever came to light about this specific incident, over half of the Democrats in Congress had already come out publicly for impeachment. The percentage of Democratic voters who are for impeachment has always been high. So this is really the triumph of the grassroots and the will of the American people building over years and demanding hold the president to account and do what’s right.”

Trump is set to join a select group in the presidential hall of shame. Andrew Johnson and Bill Clinton are the only two presidents to have been impeached, although both were acquitted by the Senate. Richard Nixon resigned under the threat of impeachment.

Steyer, an entrepreneur, shares the view that Trump may be vulnerable.

“If the American people hear the evidence and decide, ‘He’s a liar and a cheat, if I did this I’d be in jail,’ then I think all of the senators, including the Republican senators, are going to have to look in the mirror and decide: can they really go against what’s right, go against the constitution and go against the American people?”