I've got a question as a non-American. In the UK, yeah it's not a duopoly like the US is but after the election the leader of the opposition still plays a large role in Parliament as the Leader of HM Loyal Opposition.
What happens in America? What happens to the presidential candidate who looses the election. Where do they stand in their party and do they still hold a position?
We do not have party-based elections and we do not have opposition offices. As I understand in the Commonwealth, at least Australia, there are "Shadow Ministers" which are somehow juxtaposing the Minister (which humorously has resulted in Australia's Minister of Defense being a former Shadow Minister of Justice from Batman, Australia). For the Prime Minister, you actually vote for the party and then the party picks their Prime Minister. The PM can then be fired or resign (like David Cameron did) and the Party can replace them without new elections.
In the US there's none of that shit. Our parties are basically private clubs. In the primary elections, our party (which we belong to symbolically, basically) decides their nominee for President. The primary vote is really misunderstood and are
not comparable to our general election. They are not regulated like the GE, are basically like a private club's counting of votes, and frequently the parties smudge the rules to get the establishment favorite they want anyways regardless of the popular vote and each party has had different rules for how they select their nominee. The nominee then creates a ticket with a vice presidential pick of their choosing and they make their bid for the presidency.
The only reason parties hold these primary elections is it gives people an illusion that their vote is considered. Many high-ranking officials within the GOP wanted to block Trump from being the nominee, but the voter base was so enthused about Trump at the time they knew honoring the votes was the only way to keep the Republican party together. Not doing so would have resulted in an independent Trump party stealing half of the GOP's votes, or more, and cost the election for the conservatives. Nothing legally kept them from doing this however.
In our House of Representatives and Senate, collectively referred to as the Congress, we have two groups. The Senate is precisely 100 people -- 2 from each state, Washington D.C. not included. Congress is based on population and are elected from small, arbitrarily drawn districts within each state, determined by state government. There currently are over 400 people in Congress. In order for a bill to become law, it must be approved by the Senate and the House and then be signed into law by the President. If the President refuses to sign it, it is called a Veto. Senate may vote with a 2/3rds majority to override the veto and force a bill into law. This has happened precisely once in President Obama's two terms. Congress people are up for election every 2 years, and the Senate is up for election every 6 years. This year, at the same time, both congress and senate will appear on the ballot alongside the president.
What frequently happens in American politics is that, because of the varied lengths of terms, the house / congress / president will be of different party affiliations at different times. This usually results in a lame duck where nothing gets passed. Because of Bush Jr's failures, Obama was elected into office with a democratic congress and senate, and is frequently criticized for getting relatively little done with that opportunity.
A lot of the reason the 2016 election is so contentious is not only that Trump and Clinton stand to win both the White House, the Senate, and the Congress at the same time, but our federal Supreme Court has at least 2 people coming up for immediate replacement and up to 5 people within the next 8 years. The Supreme Court is 9-member life-long appointment that must be nominated by the President and approved by the Senate. They are the single most powerful entity in our country's legal system and are responsible for upholding the constitution. A law that is passed and signed, if against our constitution, can be thrown out by the Supreme Court. They are responsible for passing
de facto laws via court precedent which dictate how all lower courts will react to similar cases.
So basically, this election is super fucking important because it's winner takes all and if the wrong decisions are made the entire country might be a mad house for the next 50 years. Since we're already on the very precipice of total global war and economic collapse, most Americans are conscious that poor choices resulting from this election may be a real mortal wound to our very livelihood and existence.