A political action is ethical if it normally would be ethical. For example, if you consider it unethical to bribe someone, then it is unethical to take a bribe as a politician. People’s ethics to matter to them, and they do decide who to vote for based on whether or not the politician acted ethically.
Politicians routinely resign due to affairs or other unethical behavior that is not directly related to their job, because people assume if you cheat in one area of your life, you will cheat in others.
"There's good evidence that men with great power and status are, in fact, more prone to affairs," says Todd Shackelford, who directs the evolutionary psychology lab at Oakland University in Michigan. (npr)
The bottom line is, if it seems shaky you should not accept it! Ethics may be personal to a certain extent, but right and wrong does matter in politics.