All the president's opponents: Donald Trump has embarked on a dangerous mission

A concerted effort to punish the whistleblower, the witnesses and those who co-operated with the impeachment probe undermines American democracy

Lt Col Alexander Vindman, a decorated Iraq war veteran, and his twin brother, Lt Col Yevgeny Vindman, were both marched out of the White House. AP Photo

Heads are going up on pikes after all (in a manner of speaking, of course).

During US President Donald Trump's impeachment trial, the lead Democratic Party prosecutor, Adam Schiff, cited reports that Republican Party senators were warned that if they wavered, their "heads would be on pikes". Republicans feigned outrage. Last week, Mr Trump was acquitted by the Senate Republican majority, which had vowed to do just that before the witness-free trial – essentially just a debate – began. Several of the so-called moderates who were indignant about Mr Schiff's "pikes" remark justified their acquittal votes by saying the president had "learned" a lesson and would be chastened.

That would be a rational response. But less than 48 hours after the verdict, the president initiated what will almost certainly be an extended campaign of vengeance against his perceived enemies. First to go were two key witnesses against the president and, to add an appropriate level of fear, an innocent bystander.

Few will weep for Gordon Sondland, just fired as US ambassador to the European Union, who donated $1 million to Mr Trump's inauguration festivities. He is unlikely to get a refund. Yet it is shocking to see anyone dismissed for merely testifying to the US Congress. Far more disturbing was the summary ouster from the National Security Council staff of Lt Col Alexander Vindman, a decorated Iraq war veteran, and his otherwise uninvolved twin brother, Lt Col Yevgeny Vindman. Both were marched out of their White House offices by armed security guards.

This first round of payback came immediately after Mr Trump railed against the "crooked", "vicious", "horrible", "bad", "dirty", "evil and sick" people who had not sided with him. His spokeswoman vowed that such people "should pay". At the annual National Prayer Breakfast, the president said he rejects the core Christian doctrine of loving your enemies and suggested that his supporters were all pious people while his opponents – including Senator Mitt Romney, a Republican who voted to convict him, and House Speaker Nancy Pelosi – simply use religion to conceal their wicked deeds.

The campaign of intimidation is plainly just beginning. Another likely victim is the whistleblower who first alerted Congress to the president's efforts to coerce Ukraine into announcing an investigation into Joe Biden, Mr Trump's possible opponent in the 2020 presidential election, and his son. Indeed, Senator Rand Paul – a Trump ally – has been attempting to expose this whistleblower by name, making further punishment possible. Also at risk is the inspector general of the intelligence community, Michael Atkinson, who allowed the whistleblower's complaint to be passed to Congress – as legally required.

The Vindmans, the whistleblower and Mr Atkinson all followed the law and did their duties. But they enraged Mr Trump and so must “pay". Many other officials could similarly be in jeopardy. Republican senators are preparing hearings against Mr Biden and his son. Officials from the Department of Justice are being investigated for having themselves investigated the Trump campaign. And the administration is reportedly searching for ways to strike back at Mr Schiff, Mr Romney and Ms Pelosi, among others.

Mr Trump claimed "full vindication and exoneration" by the Senate. But, in fact, not only was the trial a mockery of any judicial proceeding, and the only Senate trial in US history in which no witnesses were allowed, many of the key senators who ultimately sided with him acknowledged that Democrats had proven their case and that what the president had done was inappropriate, troubling and wrong. Yet except for Mr Romney, all concluded the correct response was to acquit Mr Trump and endorse his re-election.

Meanwhile, Mr Trump seems not only un-chastened, but enraged and even emboldened. He has specialised in using the powers of his office to attack his perceived enemies in an unprecedentedly personalised and vindictive manner. For example, he repeatedly urged his officials to persecute and legally prosecute his opponents, particularly Hillary Clinton, his presidential opponent in 2016, and James Comey, the former FBI director.

Republicans in Congress show few signs of discomfort with the budding retaliation campaign, and those that have urged caution were reportedly rebuffed. The president has plainly drawn the inevitable lesson. Throughout his life he has relied on bluster, bullying and threats and has got away with skirting laws, norms and conventions. And most of his supporters will cheer the persecution of the likes of Lt Col Vindman, his brother and the whistleblower.

One important democratic guardrail still standing is the November election. Mr Trump's popularity numbers are robust and the sound economy he inherited from Barack Obama remains hardy. Besides, having just got away with an attempt to subvert the coming election, Mr Trump might be tempted to try again.

If he is re-elected by whatever means, there is every danger that the accelerating slide towards American autocracy could well be completed.

Hussein Ibish is a senior resident scholar at the Arab Gulf States ­Institute in Washington