It is a memorable retreat for National Security Adviser John Bolton after a year and a half in office. Known as a "hawk," he was a foreign policy hardliner who always openly demanded military strikes and who, above all, was decidedly against any form of diplomacy with political opponents.

As tough as his positions were, John Bolton was also someone who always stood in the way of President Trump's impulsiveness. With him gone, another critical voice falls silent in Trump's circle and will probably be replaced, as has often been the case before, with a loyalist.

Changing the Cabinet in record time

Take Attorney General Jeff Sessions, who refused to dismiss the inconvenient special counsel Robert Mueller and declared himself compromised in the Russia investigations. Urged to step down, President Trump replaced him with the far more agreeable William Barr, who immediately caused an outcry from the Democrats with his skewed interpretation of the Mueller report, clearly having his boss's back.

There was also the resignation of the highly experienced Defense Secretary Jim Mattis, who threw in the towel after Trump announced the withdrawal of US forces from Syria, taking many of his advisers by surprise. Mattis had been considered one of the last voices of reason in Trump's Cabinet.

Bolton cannot really be called a voice of reason. As one of the architects of the Iraq War under George W. Bush, he can easily be accused of destabilizing the entire Middle East with his actions. More recently, he demanded Trump make a military strike against Iran. Although Bolton, like President Trump, is an opponent of multilateralism, his saber-rattling contradicted Donald Trump's central election promise to keep the US out of international crises and conflicts.

Meeting the Taliban on equal footing

Bolton was also unfortunately a strong critic of Trump's unsuccessful deal-making attempts, especially those in which he tried to approach foreign despots on equal footing. Trump's fruitless meetings with Kim Jong Un, for example, were a PR success solely for the North Korean dictator. And had the Taliban been invited to a meeting at Camp David, it would have put them on a par with international heads of state of distinction.

Read more: Taliban spokesman Subhail Shaheen: 'We had finalized peace deal with Americans'

The latter example was a huge thorn in Bolton's side, as he had no time for diplomacy with adversaries, particularly radical Islamists like the Taliban.

John Bolton's departure may be good news for US diplomacy, a rebuff to American warmongering, and a sign of hope for the stalled conflict with Iran.

But his fate also shows once more how Donald Trump deals with critics who stand in his way. Those who do not parrot what the president says have to go.