Trump effectively confessed to an impeachable offence last night. He should be removed immediately

A smoking gun, that is what Democrats have been searching for more than two years. In the eyes of many liberals Donald Trump's behaviour has been worthy of his removal for a while, but proving it has been difficult.

On Thursday, the president basically loaded the bullet himself and fired off a quip about China investigating Joe Biden and his son Hunter that likely left the surrounding press pack smelling cordite.

Questioned whether he had asked China's President Xi Jinping about starting an investigation into the conduct of the Bidens – of which no evidence of wrongdoing has yet been presented – Trump replied that he hadn't but that it's "certainly something we can start thinking about".

The president also noted that the US is in trade negotiations with Beijing and “if they don’t do what we want, we have tremendous, tremendous power”. In Trump's eyes a quid pro quo does not exist unless he is addressing someone directly, but the exchange with reporters proves how easily the words drop from his mouth.

For Democrats, those words should feel like manna from heaven. Impeachment is a political case likely to fall short in the Republican-led Senate, but what helps you prove such a case? When the subject repeats behaviour after having essentially been made clear of the danger.

Some will follow Trump's narrative that he has done nothing wrong – he is not denying the allegations. That an investigation will boil down to whether it is fit for a president to ask a foreign government to investigate a political rival. That muddies the water in exactly the way Trump wants. Soliciting a foreign country to meddle in an election – and if Joe Biden becomes the Democrat nominee or is close, how can that not be seen as such – is a felony.

Late last night it was reported that Trump raised Biden's political prospects with Xi during a call in June and the record of that call was stored on the same exclusive server that hosted the call with Ukraine's Volodymr Zelensky. The call now at the centre of the impeachment probe.

Everything else is just grist to the mill. But it does provide some powerful supporting evidence. Elements of the state department were allowed to assist Trump's personal attorney Rudy Giuliani to help push the investigation into the Bidens, and Trump asked for his attorney general to be involved too. Trump will also mobilise every weapon at his disposal to protect himself, meaning there will always be multiple avenues for investigators to chase up.

The text messages from officials surrounding the Zelensky call prove that. On the morning of the call between the Ukraine leader and Trump, envoy Kurt Volker informed a Zelensky aide that a visit to the White House was predicated on the president convincing Trump that he’ll “get to the bottom of what happened” in 2016. The week before, on 19 July, Volker tells another US official: “Most important is for Zelensky to say that he will help investigation – and address any specific personnel issues – there are any.”

This, and a number of other texts, show one thing. That Ukraine must be in no doubt that security assistance and aid is tied to help with the investigations Trump wants.

The president and his inner circle might deny wrongdoing, but the evidence is clear. It is not a legal test that must be passed, but a political one, and the bar has been cleared. Trump must eventually reap what he sows, but we cannot wait for the judgement to come at the ballot box.

Trump must be impeached now. Removal should follow, even if it likely won't.