But it is on the wider issues that he has shown his true worth. If we look at the world as a whole, and the choice that faces all of us as being between a democratic form of government on the one hand and tyrannies of one sort or another on the other, then we can be in no doubt where President Obama stands. He is not only an advocate for democracy but an embodiment of it.
The world is not short of critics of democracy, or of leaders who represent its antithesis. Nothing would suit anti-democrats better than to point to the world's most important democracy and to sneer at what the democratic process had thrown up. They have not been able to do that with President Obama at the helm. Here is a man of obvious ability, judgment, and good sense.
The whole democratic world, in other words, has a vested interest in the good health of American democracy. In New Zealand - as in every other part of the free world - we are safer and stronger if American democracy can provide the US with leadership of a quality that the rest of the world might aspire to.
If, for any reason, President Obama is succeeded by someone who does not meet that high standard, and who does not embody in his or her own person the qualities that are required for leadership in a democratic country, we are all weakened. There are regimes in Beijing and Moscow and in many lesser capitals who would be quick to advise their own people and anyone else who would listen that democracy cannot be relied on to deliver effective government, and that claims that democracies are somehow better at serving the interests of their people cannot be sustained.
It matters greatly, in other words, that the 2016 presidential election produces a President who, at home, can bring people together and treat every section of society - in racial, gender and economic terms - with respect and consideration and, in the international sphere, can exercise calm and considered judgment, and can be relied on to provide help and friendship to all those across the globe who share democratic values.
And, as President Obama has shown, if the US President is to be treated as the de facto leader of the free world, he or she must embody in his or her own life the values that a great democracy holds dear. The holder of that office must be seen as worthy of our trust, must act with dignity and respect for others, must represent the interests of all the people and not just the rich, famous and powerful.
We - and by "we" I mean democrats across the globe - need a President we can respect. When the American voter casts a vote for the Presidency, it is a vote that has consequences far beyond American shores. It is a decision for the American voter alone but it matters to all of us. We need to get it right.