I guess that raises two questions. First of all, just how corrupt is our present system. And second, just how corrupt is Donald Trump.
As for corruption in our present system, there are several ways to look at it.
One interpretation of corrupt is the crudest sense of corruption, i.e., are our politicians being flat-out bribed? Well, there was William Jefferson and his fridge full of money, but so far as I can tell, this is an unusual case. For the most part, there isn't that much flat-out bribery going on. Corruption in our political system is something more subtle.
At the other end of the spectrum is the politiphobe definition of corruption, which basically amounts to the existence of politics at all:
[Politiphobes] believe that obvious, commonsense solutions to the country’s problems are out there for the plucking. The reason these obvious solutions are not enacted is that politicians are corrupt, or self-interested, or addicted to unnecessary partisan feuding. Not surprisingly, politiphobes think the obvious, commonsense solutions are the sorts of solutions that they themselves prefer.Only slightly less sweeping is the concept of corruption implied in the whole uproar over the Hillary Clinton e-mails, which roughly defines corruption as networking. I noticed much the same thing all the way back in 1997 at the time of the Southeast Asian economic crisis. The general consensus seemed to be that the Asian economies crashed because of corruption and "crony capitalism." These terms were roughly defined to mean people making decisions based on their personal relationships, rather than cold-blooded calculations about the bottom line. In other words, acting like actual flesh-and-blood people, rather than the soulless Homo economicus that inhabits textbooks everywhere.
Let's face facts. Treating one's personal relationships as primary is simply human nature. Yes, treating important public policy decisions simply as an exchange of favors between friends is inappropriate and often corrupt. That is why there are so many elaborate disclosure and anti-corruption rules, to keep basic human nature from asserting itself. But in the end, such rules can only go so far. People will network, do favors for friends, exchange one favor for another, grant access based on past association and so forth. There is simply no way to prevent it short of taking humans out of government altogether and replacing them with computers.
Another extremely broad definition of corruption is acting on one's own private interests instead of for the public good. Here again, given the difficulty in figuring out what the public good is and how it is best served, as well as the mind's extraordinary ability to rationalize what it wants, it seems a reasonable assumption that corruption of this kind is impossible to eliminate. I realize that at this point libertarians would agree and say that is all the more reason to hold government to the absolute bare minimum (roughly, a criminal justice system and civil courts to enforce contracts), to prevent that sort of corruption and abuse of power. My only response can be that I think libertarians seriously underestimate how much corruption and abuse of power can take place outside government.
My answer, instead, is that if you can't eliminate corruption of this kind, your better bet is to broaden or, if you will democratize it. My own hypothesis is that the broader the corruption, the more people who benefit, the broader the interest being promoted, the less it differs from the public good, and the less noxious the corruption.
Consider some points of comparison. At the time this country was founded, corruption was rife in Great Britain. One form this corruption took was in representation in Parliament. Representation was not in proportion to population. Some district had only a handful of eligible voters (rotten boroughs). Election from this district could be achieved simply by bribing a handful of electors. In other districts, one wealthy proprietor permanently had power to bribe or coerce the view eligible voters ("pocket boroughs" because they were in a proprietor's pocket) to ensure his election to Parliament. Bribery of this crude sort was not possible in districts with large populations. This is not to deny that bribery is possible. A longstanding US tradition has been for representatives to bribe their constituents with "earmarks" and pork barrel projects, i.e., bringing popular public works to the district. This, too, is a form of bribery, but it is one in which a fairly broad swath of the population benefits and therefore, I would say, a less noxious one.
The US Congress in 1995 under the leadership of Newt Gingrich is another case in point. Republicans had denounced the Democrats as the party of special interests and taken power proudly boasting that they had no such corruption. They then proceeded to attempt to turn Congress into a wholly owned subsidiary of the Chamber of Commerce and introduced legislation to block the introduction of modern anti-bacterial methods of food inspection, to make it easier for companies to dip into employee pension funds, to sell National Forests to mining and timber interests, and so forth. My mother commented at the time that this showed that Republicans were just as must the party of special interests as Democrats, their interests were merely narrower. The AARP (America Association of Retired Persons) represents only a sub-portion of the population (retirees) whose interest can legitimately conflict with the interests of working age people. But it is a much broader, and therefore less noxious, interest than the ones who wanted to dip into employee pensions and so forth.
All of which leads to a specific kind of corruption of this kind. Namely, elites the world over (the 1%, if you will) have a marked tendency to confuse their own power and privilege with the common good. The US is no exception. In the US, this means a tendency for our elites to believe that whatever maximizes profits maximizes the public interest. It informs the Republican Party's insistence that cutting taxes as the top and gutting regulations should always be top priorities. Critical here is many people's belief that the 1% have captured our politics altogether and that popular voices have been completely shut out.
This is very much the fear of people on both sides of the aisle. Followers of Bernie Sanders and followers of Donald Trump share it, though in different ways. To Democrats (myself included) the all-consuming hegemony of the 1% is shown in the Republican obsession with cutting taxes at the top and gutting regulation, and the obsession of Very Serious People in balancing the budget by cutting entitlements. To Republicans, the all-consuming hegemony of the 1% is shown in Republican willingness to admit more immigrants who will add cheap labor, in the Supreme Court ruling in favor of same sex marriage, and in the current atmosphere that treats people to oppose same sex marriage and giving transgenders access to the restroom of their choice as outside of all bounds of reasonable discourse. And people on both sides of the aisle see it manifested in this endless insistence on intervening in wars in the Mideast long after such interventions have proven fruitless.
Is this true? Well, I believe that the 1% have a much stronger grip on our body politic than before, partly be campaign donations, and partly by the decline of many interest groups that represented people outside the 1%, like labor unions. But it would be false to say that our political class are completely unresponsive to pressure from below. For instance, Trump supporters still act as if the Republican establishment favored unrestricted immigration, when that simply is not so. By now securing our border and opposing any path to legalization are essential ideological tests for a Republican almost as much as tax cuts at the top. And make no mistake, this is the result of pressure from below. The same applies to guns. Another basic ideological marker for Republicans is opposition to any sort of restriction on firearms ownership, also the result of pressure from the rank-and file. The same applies to church members and abortion.
On the Democratic side, raising taxes on the top rates seems unlikely to be the result of the views of the donor class. And while it does seem fair to say that the donor class are lock-step in favor of same sex marriage and trans-genderism, that, too, ultimately came about from pressure from below. So, too, Black Lives Matter is a seeking to exercise influence from below. In short, it is still possible to exert pressure from below and influence politicians; it is just more difficult than in the past.
Another aspect of our political system that is both a source of corruption and a limitation on the power of the 1% is that the 1% is by no means a monolith. Not only do elites tend to identify their interests with the common good, but they are divided into sub-factions that each equate its own particular interests with the common good. For instance, the finance industry identifies the common good (savers!) with maximum return on passive investments (raise interest rates); extractive industries identify the common good with repealing environmental regulations; real estate developers identify the common good with repealing land use regulations; manufacturers (often) identify the common good with protectionism, and so forth. Furthermore, these interests are not just interests of the 1%. Many people work in all these industries and share vertical ties with the people at the top; thus the whole industry from top to bottom shares common interests. (There are also conflicts within industries as well, of course, such as labor-management conflicts). This might be seen as combating one form of corruption (the horizontal interest of the 1%) with another kind of corruption (the vertical interest of particular industries).
So what about Donald Trump? Well, I just finished watching his second debate, and he has definitely put emphasis on this -- that Hillary is captive to her donors, while he is too rich to buy. And he took her to task for the fact that she had been in government for 30 years, yet the country still has problems. If he were elected President, he would fix all of them. That is, quite simply, an appeal to the politiphobe view of corruption, that the mere existence of politics is corruption, and that if we could set aside the failings of politicians, everything would be fixed. It is, of course, a fantasy.
But the thing about Donald Trump is that his record indicates him to be corrupt in the narrowest possible sense, and therefore the most dangerous. He is not a candidate who equates the public good with the interests of the 1% or the interests real estate development. He gives no evidence of having any concept of the common good apart from his own interests. He is a candidate who takes advantage of the Brexit to pitch for his golf courses in Scotland. He is a candidate whose campaign routinely buys Trump products and uses Trump buildings and pays Trump enterprises inflated prices for the privilege. He is a candidate whose concept of putting his wealth in blind trust is turning his business empire over to his children to manage.
This is, I think, what most people think of when they talk about political corruption, certainly what many fear is what our system has become. And Trump is running as the candidate who will put an end to this type of corruption -- by embracing it whole-heartedly.