看懂文章《美国初选和党团会议》（https://www.bbc.com/news/world-us-canada-51273719）之前，筒子们需要解决2个单词：primaries和caucus。文章先给出caucus的定义：
Caucus：
A caucus involves people attending a meeting - maybe for a few hours - before they vote on their preferred candidate, perhaps via a head count or a show of hands. Those meetings might be in just a few select locations - you can't just turn up at a polling station.
在词典里caucus的意思是：
“A meeting of the local members of a political party especially to select delegates to a convention
or register preferences for candidates running for office.”（党团会议），在这段话我们可以看出党团会议的几个特征：1. 数人头数或举手投票，因此不匿名；2. 有规定的投票站；3. 有规定的投票时间。
Primary:
Unlike a caucus, where voters are expected to turn up at a few limited locations at certain times and stick around for a while, primary voters can just turn up at a polling booth and vote in secret. Then leave.
在词典里primary的意思是“the process by which voters can indicate their preference for their party's candidate, or a candidate in general, in an upcoming general election, local election, or by-election, with the goal of narrowing the field of candidates.”（党内初选）。党内初选不同于党团会议，投票人投票更为自由，党内初选的特征有：1. 匿名投票；2. 投票站更多；3. 投票时间更自由。
因此，两者的区别可以这样来说：caucus更侧重于党员投票决定，是由各政党自己举行的内部会议；而primary可以是开放式初选（非党员和注册党员均可投票）和封闭式初选（注册党员投票），强调的是“匿名投票”。
但是2者最大的共性就是都是为了选取候选人参加竞选，每个州的初选或党团会议通常为间接选举，选民并非直接决定总统候选人，而是选出候选人参加各党提名大会。这些代表则会在大会上选出各党总统候选人。
那么美国大选的运作形式是怎样的呢？通过文章我们可以看到：
每个州或地区先通过一系列的初选和党团会议选择候选人，2月3日先从爱荷华州开始，6月初在波多黎各自由邦结束。
今年共和党候选人是特朗普，虽然从理论上来说他在党内会有一个对手，但是由于特朗普在党内的高支持率，今年共和党内的竞争可能并无看头。了解了这一点，民主党内的初选就显得大有看头了。
过去一年，民主党内有28名候选人宣布竞选总统候选人。但是由于资金不断缩水、公众反响不温不火甚至有些冷淡以及互相攻击，最后参加竞选的只有11人。目前，这一数字已减至7人。
2月3日最先从爱荷华州开始的是一系列的党团会议，而非初选。伯尼·桑德斯和皮特·布蒂吉格在爱荷华州的党团会议上都有不俗的表现。今年，民主党仅在美国的4个州（内华达州、北达科他州、怀俄明州和爱荷华州）有党团会议。在任一一场党团会议或初选中，候选人得票率不得低于15%。当所有候选人得票率都低于15%时，党员可进行第二次投票。
爱荷华州重要吗？
为何初选先从爱荷华州开始？这就不得不提到美国第39任总统吉米·卡特。1976年卡特竞选总统之时，其竞选团队意识到先从爱荷华州竞选可以抓住先发优势。果不其然，卡特在爱荷华州的大获全胜让其势不可挡，最终成为一匹黑马当选美国总统。至此，爱荷华州成为候选人初选首发的必争之地。
爱荷华州不重要吗？
爱荷华州虽然从以上角度说很重要，但是它又没那么重要。自2000年以来，许多在爱荷华州获胜的候选人都没能最终成为总统候选人。
上述讲到了从爱荷华州开始的是一系列的党团会议，而非初选。那么第一次初选是从哪个州开始的呢？新罕布什尔州。2月11日，位于美国东北部、仅有130万人口的新罕布什尔州再次成为政治斗争的温床。经过新罕布什尔州一役后，乔·拜登和伊丽莎白·沃伦大有可能成为民主党候选人，尽管贝尼·桑德斯和皮特·布蒂吉格在新罕布什尔州获得的党代表票数最多。
好戏将于“超级星期二”3月3号开始
3月3日是初选日历上的大日子。届时将有16个州和地区、达2/3的党代表为候选人投票。这天结束后，民主党候选人将愈加明朗。
加利福利亚州和德克萨斯州是16个州和地区中拥有最多党代表的两个州。其中，加利福利亚州有415名党代表，德克萨斯州有228名党代表。这两个州的人口非常多样化，因此这两个州的投票结果和爱荷华州、新罕布什尔州相比会有较大差别。
3月3号“超级星期二”过后，3月10号的星期二会成为又一个重要的日子。这一天将有6各州、352名党代表投票。
特朗普大有可能于8月24至27号在北卡罗来纳州夏洛特市召开的党大会上宣誓成为共和党候选人，民主党则会于7月13至16号在威斯康星州密尔沃基市召开的党大会上确认党内候选人。
关于党大会
假设在初选季，A候选人获得了10个党代表的支持。那么，在党大会期间这10个党代表就会支持A候选人成为民主党候选人。（任何一个党员都可申请成为党代表，党代表一般是党内积极分子或当地政治领导人。）
民主党初选过程共有3979名党代表。候选人在初选季若获得超过50%也就是1990名党代表的得票数，将在党大会上成为党内候选人。但是，如果候选人在初选季没有获得超过50%的党代表支持率，就会出现“争议大会”或“协商大会”的情况。解决的方法就是再次投票。
不同的是，再次投票过程中会加入771名“超级代表”。往届或现任党内高级官员都有可能成为“超级代表”，如前总统比尔·克林顿，现参议员佛蒙特和总统竞选人贝尼·桑德斯。“超级代表”可自由投票。在再次投票过程中，候选人必须获得50%也就是2376名党代表的得票数才能成为党内候选人。
上一届总统大选，“超级代表”在党大会第一次投票时和普通代表一起投票。但是很多代表在大会开始之前就已经是希拉里·克林顿的死忠粉了，认为该制度极不公平的贝尼·桑德斯于是开始推动变革。这一次，贝尼·桑德斯或许能够从中受益了。
总统大选
党大会之后，总统候选人离成为总统仅一步之遥——于11月3号举行的总统大选。
英文原文
US election 2020: What are primaries and caucuses and how do they work?
Four years after the world watched Donald Trump's momentum build and build until he became the Republican nominee, America is again deciding who will run for the White House.
The nominees are being chosen through a series of primaries and caucuses in every US state and territory, that began in Iowa on 3 February and ends in Puerto Rico in early June.
The Republican nominee will be Donald Trump. Even though technically he has a challenger, he is so popular among Republicans, he has a clear run ahead of him. With that in mind, the Democratic primaries are the only ones worth watching.
It's an unusual process, not all of which makes sense, although we've tried.
Step one: The start line
A whole year before the primaries, the first candidates emerged from hibernation. Over the year, others woke up and eventually 28 people announced they were running to become the Democratic nominee for president.
But dwindling funds, luke-warm or (ice-cold) public reaction and campaign infighting have, to varying degrees, led to most of them pulling out of the race.
At the start of primary season, 11 people remained in the running, a number that has now reduced to seven. In theory, any one of them could become the nominee. In reality, only a few have a chance.
Step two: The Iowa caucuses
The first event of the primary season isn't a primary at all - it's a series of caucuses, in Iowa. These took place on Monday 3 February, in somewhat chaotic fashion.
What are caucuses?
A caucus involves people attending a meeting - maybe for a few hours - before they vote on their preferred candidate, perhaps via a head count or a show of hands. Those meetings might be in just a few select locations - you can't just turn up at a polling station.
As a result, caucuses tend to really suit candidates who are good at rousing their supporters to get out of bed. People like Bernie Sanders, for example, who performed well in Iowa this time, as did Pete Buttigieg.
Caucuses used to be far more popular back in the day, but this year, Democrats are holding only four in US states - in Nevada, North Dakota, Wyoming and Iowa.
If any candidate gets under 15% of the vote in any caucus, their supporters then get to pick a second choice from among the candidates who did get more than 15%, or they can just choose to sit out the second vote.
Why does Iowa matter?
A win there for any candidate can help give them momentum and propel them to victory in the primaries.
Why is Iowa first in the primary calendar? You can blame Jimmy Carter, sort of. Iowa became first in 1972, for various technical electoral reasons too boring to go into here. But when Carter ran for president in 1976, his team realised they could grab the momentum by campaigning early in Iowa. He won there, then surprisingly won the presidency, and Iowa's fate was sealed.
Why does Iowa not matter?
Iowa doesn't represent the entire US - it's largely white, so the way people vote there is very, very different than in other states.
Its record on picking the eventual nominees is a bit rubbish too, at least when it comes to Republicans - when there's an open Republican race, Iowa hasn't opted for the eventual nominee since 2000. Such names as Mike Huckabee, Rick Santorum and Ted Cruz have won there in recent years.
This year, Iowa suffered a bloody nose when the Democratic result was delayed by days due to technical glitches. Its curtain-raiser status may now be in doubt.
Step three: The New Hampshire primary
Eight days after Iowa on Tuesday, 11 February, was the first primary, in New Hampshire. The tiny north-eastern state of only 1.3m people once again became an unlikely hotbed of political activity.
What is a primary?
Unlike a caucus, where voters are expected to turn up at a few limited locations at certain times and stick around for a while, primary voters can just turn up at a polling booth and vote in secret. Then leave.
How does a primary work?
The more votes a candidate gets in a caucus or primary, the more "delegates" they are awarded, and all candidates will be hoping to win an unbeatable majority of delegates.
The number of delegates differs in each state, and is decided by a convoluted series of criteria. In California's primary, for example, there are 415 Democratic delegates up for grabs this year. In New Hampshire, it was only 24.
This year is a bit different. Any candidate would need to get at least 15% of the vote in any primary or caucus to be awarded delegates. There are still eight candidates in the running - an unusually large number - so there's a risk the vote share will be spread out and some of the candidates may struggle to reach 15%.
After New Hampshire, we started to get a clear picture of who was struggling (Joe Biden, Elizabeth Warren), but even though Bernie Sanders and Pete Buttigieg had claimed the most delegates at this stage, neither is guaranteed to become the nominee.
The picture should become much clearer on...
Step four: Super Tuesday
A few other states vote in between New Hampshire and the end of February, but this is when things really start to warm up: Super Tuesday, on 3 March.
What is Super Tuesday?
It is the big date in the primary calendar, when 16 states, territories or groups vote for their preferred candidate in primaries or caucuses. A third of all the delegates available in the entire primary season are up for grabs on Super Tuesday. By the end of the day it could be much clearer who the Democratic candidate will be.
The two states with the most delegates are voting on Super Tuesday - California (with 415 Democratic delegates) and Texas (228). California is voting three months earlier than in 2016, making Super Tuesday even more super than normal.
California and Texas are two states with very diverse populations, so we may see them going for very different candidates than those chosen in Iowa and New Hampshire.
Step five: The rest of the race
After hectic Super Tuesday, everyone gets to cool down for a week, before another busy day on Tuesday, 10 March, when six states vote, with 352 delegates available.
After that, the primary season still has three months left to run and at the end, the role of those delegates will become clear...
Donald Trump will almost certainly be sworn in as the Republican nominee at the party convention in Charlotte, North Carolina, between 24 and 27 August. The Democrats will confirm their candidate at their own convention between 13 and 16 July in Milwaukee, Wisconsin.
What happens in a convention?
Here's where those delegates come in.
Let's say that during primary season, candidate A wins 10 delegates. During the convention, those 10 delegates would vote for candidate A to become the Democratic nominee. (Any party member can apply to be a delegate - they tend to be party activists or local political leaders.)
All through the Democratic primaries, there are 3,979 delegates available. If any one candidate wins more than 50% of those delegates during primary season (that's 1,990 delegates), then they become the nominee in a vote at the convention.
But if we get to the Democratic convention and no-one has more than 50% of the delegates, it becomes what's known as a "contested" or "brokered" convention. This could well happen this year. There are so many candidates that no one frontrunner emerges in the primaries, and they split the delegates between them. In that circumstance, a second vote would follow.
In that second vote, all the 3,979 delegates would vote again, except this time they would be joined by an estimated 771 "superdelegates". These are senior party officials past and present (former president Bill Clinton is one, as is current Vermont senator and presidential contender Bernie Sanders), and they're free to vote for whomever they wish.
If a candidate wins 50% or more in that vote - 2,376 delegates - then they become the nominee.
This is all thanks to a rule change in 2020: last time around, the superdelegates voted at the start of the convention, with the delegates. But many had pledged their support to Hillary Clinton even before the convention, leading her rival Mr Sanders to suggest the deck was stacked against him.
He's the one who campaigned for the change - and it may benefit him in 2020.
Step seven: The presidency?
After inching past Iowa, negotiated New Hampshire, survived Super Tuesday and come through the convention, there is only one step left for the nominee: the presidential election, on 3 November.
We'll explain how that one works a little closer to the time.
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