Singapore, Jan. 18 -- Indonesia's President Joko Widodo sent a strong signal to China by flying to the Natuna Islands last week during a stand-off between Indonesian warships and Chinese Coast Guard vessels and fishing boats.

It was his fourth visit to the regency, which is part of Riau province, and came after Indonesia asserted that its territorial integrity was not negotiable. That declaration was issued in the face of Chinese encroachment into Indonesia's exclusive economic zone (EEZ).

Mr Joko's visit was a presidential gesture par excellence. Countries are judged ultimately by what their leadership does. In a presidential system such as Indonesia's, this means that they are viewed through the actions of the president and the Cabine...