As an outsider I see to main problems with the US constitutional system. One is the two-party system that leaves a lot of opinions unrepresented. Another is the influence of money on politics that prevents ordinary citizens from taking part in the political process as anything other than spectators.
I see you're from Denmark. The problem with some of your suggestions is that the U.S. political system has evolved vastly different from the parliamentary democracies of Europe. I've studied some parliamentary systems, so I would like to point out some differences.
I think a proportional system of election is the most fair. With the current system if the Democrats get 51 % of the vote in all districts they will get 100 % of the seats while the Republicans will get none. This results in a congress that provides a very poor representation of the views amongst the voters.
That's not quite the case. Our legislature is divided into two chambers: the House of Representatives and the Senate. The House of Representatives is capped at 435 members and elections are held every 2 years. The Senate is comprised of 2 per state (currently 100) and elections are held every 6 years, but are staggered so that 1/3 of the Senate is elected every 2 years.
In order to pass laws, the House and the Senate must pass the same bill in their chambers. If the House and Senate can't reconcile a bill, it dies in Congress.
This makes it HIGHLY unlikely that one party will shut out all the rest.
With regards to the Senate, if you get all Democrats voted in an election year, that's only 1/3 of the Senate; the Republican Senators elected 4 years ago and 2 years ago still retain their seats. This gives the Senate more stability than the House.
The reason why this will never happen in the House of Representatives is because Representatives aren't elected on a national basis; they are elected within a congressional district. Districts are redrawn every 10 years based on numbers from the census. Basically, the census determines how many House seats a state gets and then leaves it to the state legislatures to redraw district lines. This is to preserve the nature of federalism between the state governments and the federal government. It also means that, for instance, while the Democrats may hold a majority in U.S. Congress, the district redrawing could be done in a state where the Republicans have a majority in the state legislature.
Drawing congressional districts is a bipartisan affair, and there's great care in drawing lines around "safe" neighborhoods. For instance, they try to cram all the Democratic voters together with all the Republican voters. This tends to maximize their votes. Also, it's pretty standard fare that redistricting be challenged and go to the courts so a judge can make sure no gerrymandering happened.
In a proportional system a party will receive a fraction of the seats in parliament similar to the fraction of votes they get. This creates a parliament with more parties represented and gives voters more choice.
Like I mentioned, the U.S. political system is different. In some parliamentary systems, voters elect politicians to represent them in the national government. So, for example, if 33% of the U.S. are Democrats and 39% are Republicans and 27% are Libertarians and 11% are Greens, then the number of seats in parliament are divided up to accommodate so that all political parties represent the national political mood proportionally.
The U.S. is not like that. Representatives represent a single district and the Senators represent the entire state. This was originally done so that the local interests of the people and the interests of state governments would dictate Congress.
Of course legislation would have to be made by coalitions but the practical problems involved with these are neglible and the proportional multi-party system works efficiently in many countries around the world.
You're right, it does. But America tends more towards simplicity rather than efficiency and it's difficult to change our ways. Besides, proportional systems often violate the "one man, one vote" principle we are used to, and under a system like IRV people are given more than one vote. That's why the winner-take-all system continues to flourish - courts have a hard time validating other voting systems that would better allow multiple parties.
Proportional representation is a bit more different when electing someone for single offices such as president or governor. The solution used in many parts of the world is to have two election rounds. All candidates compete in the first round. If no candidate receives more than 50 % of the votes cast a second round is held where only the two candidates who received the most votes competes.
We have the Electoral College for voting for the President. Basically, each states get a number of electoral votes equal to their Representatives and Congress. While how those electoral votes are allocated are up to the states to determine, for the most part whichever candidate receives the most votes in a state gets all the electoral votes from that state. Whichever candidate gets 50%+1 of the electoral votes becomes President.
There's a lot of call for reforms from the Electoral College because of influence of large swing states, but it also prevents urban-centric control of the Presidency.
Systemic corruption and influence of money in politics is also a severe stain on American democracy. When politicians are dependant on money from big contributors they will take the special interests of these groups more serious than the interests of their constituents.
Thus a cap on campaign contributions has to be made so that you can only contribute a certain amount to a campaign. This amount should be so small that all will be able to afford it.
Well, here's a problem with the United States as compared to some other parliamentary systems. Here in the U.S., we have a freedom of speech. The Supreme Court has ruled that money is a form of free speech. The argument is that limits on campaign contributions won't limit politicians, it will limit the voters who support them.
Yeah, this definitely DOES give a lot of clout of our politicians to corporations. However, corporations and businessmen have just as much say in our politics than everyday laborers. If labor wanted more clout, they'd have to organize into unions and use the income from dues to contribute to politicians they're sympathetic to.
This should be combined with government funding for campaigns. All parties or candidates running for election should receive a set amount to campaign for. This should be the same amount for all as the results of elections should depend on how much the ideology of the parties and candidates appeal to voters - not on the amount of money the candidate has.
Why should politicians who are not equally popular receive only equal amounts of funding? That would be the argument against. Those candidates who are more popular will get more funding. Those candidates that are extremist politicians won't receive any funding and will never rise to make a mess of things.
Also, Americans have an innate trust of government and think politicians already get too much from taxpayer revenue. Why should we have our taxes pay for their campaigns?
Also, candidates are not the only ones who do the campaigning. PACs and other political groups often run their own ads to support candidates they support. So even if you limit a candidate's government spending you can't limit the spending a political organization does for political candidates. Freedom of speech.
To reduce the costs of campaigning - and thus allow the possibility for new parties to enter the political process - it should be considered to ban political TV ads. They cost a huge amount of money and provide little real information. Instead the air time should be used for debates and critical interviews with candidates from all parties.
Banning TV political ads would be an intrusion against people's freedom of speech, so it's NEVER going to happen. It doesn't matter how much it costs - that's up for the free market to decide. It doesn't matter how much real information it has - lawsuits can be filed if there's any defamation. It's not the news media's job to provide interviews from all parties - it's the job of the news media to bring in ad revenue for their shareholders. If a voter wanted to learn all the aspects of an issue it's up to the voter, not to the media and CERTAINLY not to the government, to research it for himself.
(note that the above aren't necessarily my own views on the subject; however, I've heard these arguments so much that I know what kind of opposition you're going to get from most Americans, especially the lawyers)