There are multiple reasons why Donald Trump ought not to be the president of the United States. However, there are only two ways of removing him from the office he has occupied for the past three years. One is to vote him out at the ballot box, which Americans will have the opportunity to do in a year’s time. The other is for Congress to impeach him, a process that began on Capitol Hill in September, and which went into public session on Wednesday, when the first hearings were beamed around the US and the world.

Although much of Washington has talked of little else for weeks, the public hearings before the Democrat-controlled House intelligence committee sharply raise the visibility of the impeachment effort with the wider public. Presidential impeachment is rare and grave. This is only the fourth time it has happened in American history. But impeachment is also both a quasi-judicial process and an inescapably political one, as anyone who remembers the 1999 trial of Bill Clinton will understand.

It is political because the 435 strong House of Representatives, where the Democrats have a majority, will have to vote on articles of impeachment against Mr Trump, probably next month. Meanwhile the 100 members of the Senate, where there is a Republican majority, will conduct any trial, perhaps in January, in which two-thirds of them must vote to convict for the president to lose his office. But the politics is all the more bitter because this is happening against the backdrop of a quickening election campaign and in an American political mood of unprecedented partisanship. This poses inescapably delicate questions for all involved.

The central issue over the coming weeks is not whether Mr Trump is a disgraceful president. The verdict on that is already in – and he is guilty. The issue is whether he has committed what the US constitution describes as “treason, bribery or other high crimes and misdemeanours”. The crux here is whether, as a whistleblower has complained, Mr Trump has used the power of his office to solicit a foreign country, Ukraine, to interfere in the 2020 US election campaign. If he did, he faces charges of betraying his oath of office and threatening US security. In the past, that might have been enough to doom him.

This week’s public hearing underscored the high irresponsibility of the administration’s action but did not provide first-hand evidence of Mr Trump’s direct role. Two senior US diplomats, old-school figures of palpable integrity from what seems like a vanished era of nonpartisan foreign service, explained how regular US policy towards its ally Ukraine became entangled in 2019 with an “irregular channel” run by Mr Trump’s lawyer Rudy Giuliani. This White House network tried to coerce Ukraine’s new president, Volodymyr Zelenskiy, to announce investigations into Mr Trump’s political opponents, ultimately without success. Against this charge, Mr Trump’s defenders offered only red herrings, conspiratorial distractions and a bizarre defence that the irregulars’ behaviour was “not as outlandish as it could be”.

The evidence so far strongly suggests that the White House was up to its neck in all this. But the next witnesses will need to move the responsibility closer to the Oval Office if undecided opinion – assuming it still exists – is to be swung behind impeachment. Mr Trump’s refusal to give evidence himself or to let his White House staff do so makes this tougher, as it is intended to. The electoral calendar plays a looming role here. The committee has little time before the election to pursue lengthy legal battles to compel witnesses to testify. Similarly, a long trial could affect the Democratic nomination contest, in which six senators are running.

Democrats were wise to be cautious about setting all this in motion. In the end, though, it also had to be done. Mr Trump’s conduct made that action inescapable; the constitution made it necessary. It seems likely at this early stage that the impeachment of Mr Trump will play out predictably. The House will impeach. The Senate will acquit. Mr Trump will claim a great victory. Both big parties will be fired up for November. The voters will then give the final verdict. Whatever the outcome, it is a very high stakes game.