For My Non-US Readers

I know that many of the Brits understand that we have non-stop elections, but others may not.
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Here is what is funny in the United States.  We have a big election every 2 years.  In Summer Olympic years, it is for President, 435 House of Representative members (the lower chamber) and 1/3 of the Senate (the upper chamber).  In Winter Olympic years, it is for the 435 House of Representative members - again! and a different 1/3 of the Senate.  (The Senate terms are every 6 years).
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The minute that the "little elections" end (Winter Olympic Years), the race for President starts anew.  So it is, essentially, a 1 year race for the nomination (for the out of office party - or both if the President is term limited out), then a second year between the 2 major parties.
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Because we have a "first past the post" system, a third party doesn't really have a chance to get into office.
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Our assemblies (the House of Representatives and the Senate) are elected in first-past-the-post districts, with no proportional apportionment additionally (for the US readers - in many countries if a smaller party gets a percentage of the vote - they get a percentage of the seats in Congress' equivalent, this helps 3rd parties get started).  And our districts are set up so they are usually reliably Democratic or Republican districts.  So most of the times, the key election is the "primary" which is also a first past the post system to determine the party's nominee.
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That is how our system is set up to produce the most crazy per captia - only the most orthodox of the candidates wins the primary - and because of the way the districts are set up - they usually win the election for Representative or Senator.  This encourages craziness on both sides.  (Aside - California, just changed this - I'll report back on how it turned out after 2012).
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Our President has a different electoral hurdle. First (during the primaries) they have to appeal to the orthodox party voters to get the nomination.  Then they need to appeal to the "swing" voters to get elected.  ("Swing voters" are a sub-group you hear about a lot.  They are like bisexuals, rumored to exist, but rarely seen in the wild.)   HOWEVER - even this is a bit of over-simplification in our Presidential Elections..
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We elect the President by block of State votes.  Each state gets a vote equal to their % of  House of Representative members (which total 435 and is attributed mainly  proportionally) + 2.
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Then the Presidential vote is first past the post, but by state.  So if you win  the most votes in California you get all 55 votes, if you win Texas you get 38, if you win Wyoming you get 3, and so on for all 50 states + the District of Columbia (don't ask).  Quite often "the most" isn't even 51%,. but all state votes go to the Candidate with the most votes.
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Here is where it gets trickier.  Some states are reliably Democratic ("Blue") or Republican ("Red").  So there is no way the Republican is going to win California or New York.  Just like there is no way the Democrat will win Alabama or Wyoming.  So all that money (about $US 2,000,000,000.00 in the last election) is chasing the few "swing" voters in a few states (Ohio, Pennsylvania, New Mexico and Missouri come to mind off the top of my head). It's crazy.