In 2014, the Supreme Court, in a decision known as McCutcheon, ruled that it is unconstitutional to limit how much an individual can give in aggregate to all candidates’ campaigns and political parties during an election cycle. This ruling affects contributions that go directly to candidates, whereas the better known Citizens United decision allows unlimited campaign spending that is (supposedly) independent of any candidate’s or party’s campaign. Shortly after the Supreme Court ruling, Congress exacerbated the situation by slipping a provision into a must-pass budget bill that raised substantially the amount a contributor can give to a party committee and allowed them to give that amount to each of multiple party committees.
Contributors are still limited by laws capping the amount one can give to any individual candidate ($5,400 for federal candidates), but the aggregate limit, which was $123,200 per two-year election cycle, was ruled a violation of free speech. Furthermore, candidates and the parties have developed strategies that allow joint fundraising where contributors can write one check that will be split among multiple candidates and/or a variety of national and state party committees.
As a result contributors are now giving checks of well over $200,000 directly to candidates. Republican Representative Paul Ryan, the Speaker of the US House, has received at least 22 checks of $244,200 each. Democratic presidential candidate Hillary Clinton has received at least eight checks of $353,400 each. For the Hillary Victory Fund, the maximum donation is actually $356,100, based on maximum donations of $2,700 to Hillary for America for the primary election, $33,400 to the Democratic National Committee, and $10,000 to the federal accounts of each of 32 state Democratic parties. 
These are only the most dramatic examples of the dozens of checks over the previous limit that Ryan, Clinton, and other politicians are receiving. Several husband and wife pairs have given close to half a million dollars per couple. And some wealthy contributors have given super-sized checks to more than one of these joint fundraising efforts. 
While the bulk of the money from these huge checks goes to party committees, these party committees often make large donations to the candidate who sponsored the fundraiser. Basically, this is money laundering that circumvents the limit on what a contributor can give to any individual candidate.
The McCutcheon ruling is one of a series of Supreme Court decisions, almost all by 5 to 4 votes, that have undermined campaign finance laws and allowed huge sums of money to flow to candidates’ own campaigns, to party committees, and to supposedly independent expenditures meant to influence voters. These Supreme Court decisions appear to ignore the realities of campaign financing and the potential of large campaign contributions and expenditures to influence elected officials. They also appear to ignore the potential for outright corruption and bribery.
Although most of the media’s attention is focused on the fundraising of the presidential campaigns, big contributors tend to have even greater influence on congressional candidates and their campaigns. Furthermore, their influence on state level campaigns can be even more dramatic.
The bottom line is that these Supreme Court decisions, somewhat exacerbated by increases in contribution limits initiated by Congress, have increased the ability of a very small number of the very richest Americans to provide ever increasing amounts and portions of campaign funding. This shifts our political system away from democracy and toward a plutocracy, where the rich elites effectively rule our country.
 Vogel, K.P., & Arnsdorf, I., 5/2/16, “Clinton fundraising leaves little for state parties,” Politico (http://www.politico.com/story/2016/04/clinton-fundraising-leaves-little-for-state-parties-222670)
 Vandewalker, I., 4/25/16, “Two years later, McCutcheon fuels huge checks to politicians,” Moyers & Company (http://billmoyers.com/story/two-years-later-mccutcheon-fuels-huge-checks-to-politicians/)