Impeachment was never going to deliver the president’s scalp. “We all know how this is going to end,” Mitch McConnell, the Republican senate majority leader, told Fox News on 12 December, shortly before the House of Representatives voted 230-197 to impeach Donald Trump. “There’s no chance the president is going to be removed from office.”

House votes to limit Donald Trump's war powers amid Iran crisis – as it happened Read more

This common knowledge – that a Republican-controlled Senate would never vote to eject Trump – has gone missing among some US Democrats. In March last year, Nancy Pelosi, the veteran Democratic leader of the House, advised her fellow Democrats against impeachment: “I don’t think we should go down that path.” After three years of declaring Trump an existential threat to the nation, Pelosi knew that the Democrats would only help the president if they took action that was not only guaranteed to fail to remove him, but which would allow Trump to reprise his favourite role: Phoenix Rising from the Headlines.

But Pelosi was in a bind. Like Theresa May, she has become the manager of a process she never wanted to happen. Faced with a revolt among Democratic lawmakers who need strong anti-Trump credentials to win their congressional primaries, she eventually yielded to their determination to remove Trump via legal means. Trump’s 25 July phone call to the Ukrainian president, Volodymyr Zelensky, seemed to provide all the ingredients that the soup of the Mueller report lacked: a Mafioso-style quid-pro-quo; a tampering with the US electoral process during, as opposed to before, Trump’s presidency; and, on top of it all, the irresistible charge of cold war vintage that Trump – with his consideration of delaying the delivery of Javelin anti-tank missiles to Kiev – was endangering national security by not sufficiently escalating tensions with Russia.

Play Video Pelosi: I'll send impeachment articles to Senate 'when I'm ready' – video

There is little question that Trump committed an impeachable offence by encouraging the Ukrainians to publicise an investigation into Joe Biden’s dealings in Ukraine. But impeachable relative to what? Many presidents have committed impeachable offences in office – whether Franklin Roosevelt’s IRS auditing of political opponents, Ronald Reagan and George HW Bush’s Iran-Contra scandal, or George W Bush’s lying to ignite the Iraq war (a 2008 CNN interview has been making the rounds, in which the civilian Trump expresses disappointment that Pelosi did not try harder to impeach Bush for the Iraq war).

These comparisons make Democratic claims that to not impeach Trump would effectively mean shredding the constitution seem more than a little over-heated. However much constitutional obligation may appear to necessitate impeachment, in the end it is always a political choice.

The irony is that Trump is now impatient for his own Senate trial to start, which he reasonably expects will bring the public more to his side. During the House’s impeachment proceedings, Trump’s approval ratings rose six points. McConnell has not so much as bothered with the usual lip service about conducting an impartial trial. On 12 December, he told Fox News, “We’ll be working through this process, hopefully in a fairly short period of time, in total coordination with the White House counsel’s office.” On 3 January, he made the case on the Senate floor that the authors of the US constitution had always intended impeachment to be a deeply political affair, which is why they designated the Senate to try presidents instead of the judiciary. Pelosi, sensing the depth of the opposition, has delayed sending the articles of impeachment to the Senate, which has raised the legal question of whether Trump has in fact been impeached at all.

Facebook Twitter Pinterest ‘Mitch McConnell, the Republican senate majority leader, has not so much as bothered with the usual lip service about conducting an impartial trial.’ Photograph: UPI/Barcroft Media

Either way, the circling tactic appears doomed to fail. Even if they are armed with court orders to make crucial witnesses appear, the Democrats cannot deny Trump his favourite resource – sensational television – for much longer without wearying the public’s patience and taking the sting out of their original intent to remove him.

In 2001, the historian Perry Anderson argued that critics of US empire should have embraced the impeachment of Bill Clinton: any body blow against the imperial presidency was surely something good for the rest of the world. Today, liberals and legal scholars argue that impeachment will at least weaken the forward march of Trumpism, much as Clinton’s impeachment supposedly hobbled his chosen successor, Al Gore. The trouble is that the impeachment of Clinton resulted in the opposite of presidential impairment: his approval reached an all-time postwar high of 73% during his Senate trial.

Like Clinton’s bombing of a pharmaceutical factory in Sudan in the wake of the Monica Lewinsky scandal, Trump may have diverted some attention away from his impeachment with the assassination of Qassem Suleimani. Yet this impeachable offence – engaging in an act of war without Congress’s approval – is unlikely to be added to Trump’s bill of offences. The presidency has accrued war powers at a rate since 9/11 that only accelerated under Obama. It would now take sweeping congressional legislation to reverse the tide. In the absence of this political will, Pelosi and the Democrats have proposed an emergency bill to make any Trump-led war on Iran only slightly more difficult.

Trump may not enjoy a popularity bump like Clinton’s during his own Senate carnival, even with McConnell as ringmaster. But however much less mystique Americans attach to their presidents since Nixon and Clinton, the office still retains an aura. For the Democrats to set themselves against it, instead of concentrating their fire on an electoral victory in November, could further inflate the executive. Their best chance for cutting the imperial presidency down to size is for them to back a presidential challenger who is dedicated to the cause of restoring Congress’s war powers.

• Thomas Meaney is a fellow at the Quincy Institute for Responsible Statecraft, Washington DC