Political corruption (or even the belief that such corruption exists) makes people trust their government less. It also makes them much more cynical about the motives of their leaders and much less confident in the direction of the country. We can see all of these ideas at play in the attitudes of the Tea Party in the US today.
Many people think that government officials are in some sense "for sale" to those who donate money to them. This leads people to think that the government is acting in the interests of the donors, not of the people as a whole. This leads to a great deal of anger at government and a general lack of trust or confidence in the government.