What the hell? Underhandedness occurs because it is a useful tool when dealing with the general public and political rivals who are out of the know on a given issue. Politicians who abstain from underhandedness out of moral considerations wouldn't be recognized for their efforts any more than people who engage in underhandedness are recognized for theirs. That's also why they don't exist; because a politician who doesn't exercise some degree of underhandedness cannot maintain their power base while in opposition against those of less lofty moral dispositions. There is simply no benefit to being virtuous in politics; so far as virtue goes, fabricating its existence in your person is much easier than actually developing the psychologically and physically exhausting character qualities necessary to possess it.
And virtue really doesn't go very far. If we assumed Obama, for example, was five times more virtuous than even his most glowing proponents claim, then the 'virtue' would simply become a symbol of derision amongst his opposition, whose preexisting interests, priorities, and political frustrations would hardly be disarmed just because their rival was virtuous. That is, if they simply didn't obscure the president's virtue so that the public would not be capable of processing it, which would be just as easy. In fact, they could do both. Hence, as far as enhancing his electoral prospects go, Obama's virtue would be completely worthless from the very beginning; the people who like him would like it and the people who don't like him wouldn't like it or wouldn't recognize it.