Trump is actually doing a favour to China in eliminating Hong Kong's international status.
When Hongkong lose its shine as international city finally, other Chinese cities take over. And this will make Hongkonger losing their feel of being westernised breed of proud and mis-leaded people, and also their strength coming from backing of capitalist western countries to fight against the central government will be like evening sun setting down the horizon.
For centuries western capitalist powers and Japan fought the Chinese government in bloody wars with guns and opium and intruded with gunships in order to get a piece of China commerce trade, aiming to gain huge profits and to propagate Christianity. Today the capitalist still are at it but replaced propagation of Christianity with Western model of democracy.
The capitalists will lose a strategic foothold if Hong Kong lose its international status because right now everyone can go to Hong Kong without visa, Hong Kong is the centre of spies aiming at China.
If Hong Kong will to impose visa requirement for US and European visitors, many spy and visitors with anti-China records will find it hard to infiltrate China. Companies with dubious records black listed by China will also find that their opportunity to a slice of commerce profit from China trade gone in thin air.