As if emotional campaign messages weren’t enough, politicians now have another way to try to win over the electorate. A study in Israel shows that voters can be manipulated into changing their attitudes by being shown subliminal images of their national flag.

A team led by psychologist Ran Hassin at the Hebrew University in Jerusalem divided volunteers into two groups: those who strongly identified with Israeli nationalism and those who identified with it only weakly. They then quizzed them about their attitude to the Israeli-Palestinian conflict after showing them a brief image of an Israeli flag or a control image. …