The answer to this question is really a matter of opinion. It is not possible to determine objectively whether power corrupts all people, how much power corrupts, and whether becoming “very powerful politically” (it would be hard to define exactly when a person becomes “very powerful”) makes people unable to “maintain a sense of reality and fairness” (however that is defined).
Studies carried out in laboratory settings tend to indicate that power does tend to corrupt people to some degree. The problem is that we do not know how much they become corrupted and how much their behavior would change in the real world.
I would argue that power can corrupt people, and that people who have more power are more likely to become corrupt. However, this does not meant that all politically powerful people lose their entire sense of reality and fairness. One possible example of this would be President Franklin D. Roosevelt. This was a man who was born wealthy and who reached the (arguably) highest level of power in the United States. Even so, he maintained enough of a sense of reality to realize that the Great Depression was a serious problem (even though it didn’t affect his wealth that much) and enough of a sense of fairness to make him want to enact programs that would help the people.
Overall, I do not think that power corrupts everyone so much that they cannot “maintain a sense of reality and fairness.” However, it is impossible to really measure how much power corrupts and how much it reduces peoples’ ability to maintain a sense of reality and fairness.
A great quote you can use for your paper is "Absolute power corrupts absolutely" which is attributed to Lord Acton. He originally wrote this opinion in a letter to Bishop Mandell Creighton in 1887. The full quote goes:
"Power tends to corrupt and absolute power corrupts absolutely. Great men are almost always bad men, even when they exercise influence and not authority: still more when you superadd the tendency or the certainty of corruption by authority. There is no worse heresy than that the office sanctifies the holder of it."
This quote is often used as a starting point for a discussion on power and its ability to corrupt. One thing to figure out-- do good people get corrupted by power, or do the corrupt seek power more than other people? Or do both happen at the same time?