There are four countries in SEA that still maintain the monarchy institute: Thailand, Cambodia, Brunei, and Malaysia.
The golden rule of the monarchy is not to “directly” making any interference to the politics. For the principle that he has not been directly elected by the people.
In modern democratic system, the political leader has been democratically elected by the people. And thus, he will be accountable by the people. Which means it’s enable (1) to be criticized by the public, (2) to be investigated/observed by the public, (3) to be demoted by the public, and (4) to be brought on trial. And this is the meaning of public “accountability” — to be account-able by the people, whether such political leader is worth for the representative of people or not.
In the constitutional monarchy system, the people decide to preserve the monarchy institute, but the people don’t want to see the monarch to be criticized. So, the state endorses a law to shield the criticism of the monarchy, whether in form of either Lèse-majesté or defamation law. And because the monarch is under the concept of hereditary monarchy not by the election, there is no connection between him and the people by the process of democratic process. Therefore, it’s naturally that he should not make any direct intervention to politics.
To publicly engage in politics means that he will choose to engage in partisan politics. Which means that he will unintentionally make either friends or foes. Which is very dangerous for the monarchy institute in the long run.
Walter Bagehot, the founder of the famous English newspaper, The Economist, wisely wrote in his own book, “The English Constitution” about the rights and the role of a monarch with the government. He suggested that the monarch has the right to (1) to be consulted, (2) to encourage, and (3) to warn.
However, these “dialogues” have to be conducted in private, not in the public. Even some suggestion from the monarch in the private has to be very careful. Or else, there will be such a case like the “black spider” memos written by Prince Charles to the British government. And that will lead more criticisms to the whole constitutional monarchy regime in the end.
I understand that the monarchy institute has different influence and role, (and also form) within four different countries in South East Asia. For the most strongest one in Brunei, and the weakest one in Cambodia. Thailand and Malaysia are in between.
The role and the influence of the monarchy institute in both countries have changed from time to time. Therefore, this will contribute to the changing contemporary political landscape of respective country.