I would suggest populist.
The word tends to imply a leader willing to be responsive to the demands of the majority, whatever they may be, and often in a way that indulges basic drives.
The question places heavy emphasis on "two-faced" and "self-serving", but typically populist leaders are not excessively duplicitous (by the standards of politics, I mean), and they do serve the demands of the electorate to some degree.
It may be true that populists lack any guiding principle about what they will or will not provide to the electorate, and it may be true that they themselves are motivated by the basic indulgences which elected office provides, but this differs from what people typically understand by "self-serving".
The obsequious butler who indulges his master's whims in fear of his own employment, is not typically thought of as "self-serving". Nor is the leader who enriches or indulges himself and his supporters, typically thought of as self-serving.
From another angle, perhaps a populist leader is seen as lacking commitment to any particular policy, unlike (it is assumed) their supporters. It may be assumed that the electorate are considerably more committed to patriotism than the populist leader, and that the leader is being more instrumental than the electorate. However this may assume the electorate themselves are not being instrumental about their patriotism - if they are, then the populist leader is actually very much in tune. The leader instrumentally chooses to express patriotism simply because he thinks it will help him, and the populace cheer, simply because they think it will help them.
It may also assume that the electorate don't realise the leader is being instrumental, when the leader's freedom from ideological rigidities may be seen as part of their attraction (particularly if the electorate have recent bad experience with unpopular ideologues who don't respond to popular demands). Seemingly outrageous policies may be cheered by the populace simply because they demonstrate the leader's freedom of thought and action, and unwillingness to comply with a prevalent bogey ideology.
At any rate, populism is capable of describing all necessary features.