木村：あの市長が汚職をするなんて信じられませんね。
佐藤：本当にね。きっと魔が差したんですよ。
Ma ga sasu
Kimura: Ano shichoo ga oshoku wo suru nante shinjirare masen ne.
Sato: Hontoo ni ne, Kitto ma ga sashitan desu yo.
Kimura: I can hardly believe that that mayor was involved in bribery.
Sato: I know what you mean. I expect temptation just got the better of him.
Ma ga sasu, literally to become suddenly possessed by a devil, means to fall a victim to temptation. The ma in this expression is the same character as that in the word akuma (devil), meaning something which leads people astray, or an evil spirit that thwarts people's good intentions.
Recently, a mayor was arrested after being involved in a bribery case. A friend of mine who knew the mayor well said he couldn't believe that he'd sunk to such a level of dirty politics. My friend went on: Dare ni demo, ma ga sasu tte iu koto ga arun desu ne. (Temptation can get the better of anyone, huh?) I suppose no one is a saint, so this kind of thing is unavoidable.
On TV a while ago, I saw a report about a married woman who had been caught shoplifting at a certain department store. She wasn't at all short of money, but she had picked up something and put it in her bag without paying. When she stepped out of the store, a security guard stopped her. She started crying: Sumimasen. Ma ga sashita to shika omoe masen. (I'm sorry. I have no idea what came over me.) What she was saying in other words was that she had never done anything like this before. This expression can be very convenient because it relieves the individual of responsibility for his/her actions and lays all the blame on the evil spirit which was supposed to have taken over him/her.
When it comes to people in positions of public trust though, I must say I'd rather they did not use excuses such as ma ga sashita no dakara, yurushite hoshii. (Temptation just got the better of me, so please forgive me.)