Political systems rely on people. Thus, no political system can be immune from corruption so long as people are corruptible. However, it may be possible to craft a system that has sufficient accountability and transparency to quickly expose and eradicate corruption, but that's the best we can do (and it is not what we have now).
In a world of shortages of resources, it is human nature to get something easily and without facing any hardships. Thus it is impossible to eliminate corruption completely.
Speaking of politics, the political leaders are the ones who try to get power in any way possible, making corruption the easiest and for some places the safest irrational way. Thus corruption is inevitable.
Great men who have power and authority are almost always bad men. For example, Hitler, , look what he did, think of all those 6 millions of Jews that were killed after being forced to labour, be experimented on and be ripped and torn away from their families. Absolute power is dictatorship. Every dictator will fall in destruction. Humans cannot handle power without some degree of corruption, because they have sinful nature. Men natural take advantage of their power and authority and use it corruptly. This will always cause their downfall. They can never be trusted.
Corruption is inevitable in politics. It is possible for a politician to work free of corruption. It is impossible for all politicians to work free of corruption. This is because human nature will get the better of some people. Politicians aren't vetted for corruption the way police officers are and even a few police officers mess up and become corrupt.
Yes, corruption is inevitable in political systems, because absolute power corrupts absolutely. Humans are well, human, and because they are human, they are likely to falter when they are given power. Humans cannot handle power without some degree of corruption, because they have a sinful nature. Humans will inevitably corrupt their governments and cause their downfall.
Wherever one finds power, someone willing to corrupt a functioning system is not far away. Political systems hold a lot of power and some people can not be trusted with power. However, it is impossible to tell which people are more susceptible to corruption than others, so political systems will always be vulnerable.
Right now corruption might be inevitable but with a massive change to the way the world works it can be rid off. Robots (computers) can not be bribed into adding more votes for your party. WAIT, we are trying to live in a utopia right? If that is to be possible it must be done with change.