politician correctly assess the voters mind,but people not assessed them, why?

Because polls are not truly accurate. 300 million people in the US, how polling 1,000 and using that result accurately portrays the voters mind is rather simplistic. The only poll that counts is the one when people vote. What do I care that 700 people out of 1,000 doesn't like Bush, heck for all I know that poll was done in Vermont.

Your English grammar needs some work. I cannot understand the question.