As Congress moves into the public phase of its Ukraine investigation, the scandal has become more clear rather than more complex.

Every witness confirms a straightforward storyline with remarkable consistency: President Donald Trump placed America’s national security at risk by abusing the power of his office for personal gain. The good news so far for US democracy is that America’s public servants are protecting the rule of law and the national interest.

The bad news is that their chief opponent is the Republican Party. It is heartening to realise so many government officials raised objections to Trump’s schemes. The President’s sycophants, proceeding from a warped theory of executive branch omnipotence, believe these subordinates should have saluted smartly and moved out when the Commander-in-Chief made a decision. Instead, those officials asked whether what they were being told to do was even legal.

In a system of government by the rule of law, this is the correct response. Even former national security adviser John Bolton visibly reacted on hearing of Mr Trump’s attempt to squeeze the Ukrainians, because whatever one might think about Mr Bolton’s views, he has been around Washington a long time and likely knows trouble when he hears it.

Mr Trump’s defenders angrily reply that it is the President, not his bureaucrats, who defines the “national interest” in foreign affairs. But Trump’s apologists never explain why he changed America’s policy on Ukraine. As far as anyone can tell, the US is still a friend to Ukraine and an opponent of Russia’s invasion of the country.

Fiona Hill and Lt Col Alexander Vindman at the National Security Council, George Kent at the State Department, and others, were acting not only on what they thought were legal barriers to Mr Trump’s orders but also in accordance – at least in theory – with US policy.

So which is it? Were the bureaucrats running rogue ops, or was Mr Trump incoherently countermanding his own administration’s policy?

One could make the cowardly argument that Mr Trump wasn’t really involved at all, and instead argue that the whole business was cooked up by his lawyer Rudy Giuliani who, in cahoots with millionaire doofus-turned Ambassador to the European Union Gordon Sondland, and Acting Director of Everything Mick Mulvaney, supposedly launched some sort of plot to help Mr Trump by proving the Ukrainians framed the Russians for interfering in the 2016 election.

This is a theory getting a test drive in Washington, and it’s so stupid it almost works.

The Ukraine arms-for-smearingJoe Biden plan is so utterly needless and yet astonishingly risky, one can only imagine it coming from three guys in a booth at the Hay-Adams Hotel after too many Old Fashioneds.

Yet it makes no sense to hang out three designated sin-eaters for the administration, not least because Mr Trump himself has admitted, proudly, to shaking down the Ukrainians, repeatedly and in writing. Excuses and alternative theories have mostly fallen by the wayside.

The President wanted a foreign country to smear an American citizen for personal political gain. It’s that simple. These facts have proved no detriment to the Republican Party in its efforts to define impeachability down. Not a single Republican voted to investigate the Ukraine mess, not even some of the retiring members.

There might be some defections in the Senate at the last minute, if Democrats craft the impeachment deftly enough, but it would be unwise to hope too much for Republican rectitude at this late date. Even Republicans who could have stayed quiet have decided to see whether they can harvest some political capital by defending Mr Trump.

Most notable here is a former ambassador to the UN, Nikki Haley, who dramatically equated impeachment to the death penalty and excused Mr Trump from political execution because the military aid, in the end, was finally delivered.

Almost certainly as part of her future campaign to be Mr Trump’s political heir, Ms Haley also revealed she had wanted no part of a cabal with former chief-of-staff John Kelly and former secretary of state Rex Tillerson to keep Mr Trump from doing the kinds of things he’s about to be impeached for doing.

It is a mystery why Ms Haley thinks this makes her look anything but awful, since she is admitting both to being silent about a plot within the White House to restrain Mr Trump while also admitting that, for two years, she concealed the concerns of two administration “adults” that the United States’ President was dangerous.

This, then, is the lay of the land. The President is manifestly guilty of multiple offences against the constitution, up to and including a betrayal of his oath as Commander-inChief to keep the country safe. The Republican Party does not care one whit about either the constitution or national security. And Ms Haley would very much like you to know she will say and do whatever it takes to be elected to national office.

Our constitutional crisis continues. We will know in a matter of months whether we can overcome this moment – and the opportunists who have brought us to it.

- Tom Nichols is a US national security expert. This is a version of an article first printed in our sister paper USA Today