Eighty-eight studies reveal that fanatically right-wing people hate uncertainty, are averse to complexity and have excessive needs for order (see Psychological Bulletin, 2003, 129, pp339-75).
They dislike ambiguity, are dogmatic and unusually scared of death. They tend to have had very strict upbringings and to secretly hate their parents and authority but, rather than face this, identify incredibly strongly with them. Oddly enough, there is virtually no reliable scientific evidence about the psychology of Lefties but, alas,
I suspect it is by no means as simple as that they are merely the healthy opposite of this pattern. Loosely defined, Lefties want a society that offers equal opportunities and the placing of physical and mental welfare ahead of profit. In my experience, plenty of Lefties are rigidly closed-minded and cling unquestioningly to their ideologies. They may be just as likely to believe in strong leaders and submission to them, and to be highly aggressive towards dissenters.
At its simplest, many Lefties come from homes where one or both parents had that political view. While Tony Blair's father was a Conservative party official, a more common cause of voting for Labour would be to have had a parent who did so. On the whole, studies suggest we tend to have similar political views to parents, probably identifying with a loved figure or out of fear of contradicting them.
At a deeper level, Lefties tend to empathise with the powerless and poor. In some cases, this may be how they were made to feel by their parents and in fighting for victims, they may be sticking up for their childhood self. An interesting category are those who make massive shifts from Left to Right or vice versa (rarer). A recent study (Personality and Psychology Bulletin, 30, pp1,565-84) demonstrated that people who are very confident of their views may actually be at higher risk of U-turns. Whereas most of us tend to seek evidence to support our opinions, the very confident like to engage with contrary facts, believing rebuttal of them will increase the strength of their position and are sure that nothing can shake their edifice. In fact, the study shows this makes them more prone to attitude change than people who avoid contradictory information.
Of course, pathologising political beliefs, even those of Bush or Blair, is a dodgy enterprise at the best of times. What is an emotionally mature response to the international economic inequalities, ecological destruction and psychological unsustainability of our present world? It took extreme violence and the killing of many innocent people to deal with Hitler. Numerous books have been devoted to what a nutcase he was, but there have been quite a few, too, devoted to the helpful role played by the depression of his main vanquisher, Churchill. Maybe pathology in a leader, whatever their political complexion, is not always such a bad thing.
RD Laing pointed out it's highly debatable whether the politician who is contemplating the use of a nuclear bomb is less crazy than the schizophrenic who claims to have one in his stomach, but sometimes you need someone in charge who is mad enough to do a terrible thing. Who knows, history may still conclude it was right to invade Iraq.