The US Constitution was set up to mirror the British Parliament in the respect that the House of Representives (the Lower House) were elected by the people (men who owned property) and the Senate (the Upper House aka House of Lords)were elected by individual state legislatures. It was not until 1920 that the US Senate were elected by the people. Certain major US Senate leaders in the past three years have advocated going back to the old system stating that the People are just too ignorant of US law. Today the House of Representives and the Senate are elected by the People regardless of sex, property status,etc. It is extremely rare to have a US Senator elected to be President. The last Senator to be elected was John F. Kennedy in 1960. Anyone is eligible who is at least 35 years old and a native born citizen who has resided at least 14 years of their life within the US. There is nothing barring former Sen. Obama from the Presidency, he's already been elected by the Electoral College who base their votes on the results of the Popular Vote by law. Obama could take a job as a dog catcher in the mean time and still be inaugurated in January 2009.

Simply put: The US government is made of 3 branches. The Congress has 2 houses, one of representatives and one of senators. These are elected from districts and states. The majority political party does not have to be the same for both houses since these are all individual elections. The President is elected separately from the Congress in a national election. We have an odd indirect election through something called the electoral college, but normally the candidate receiving the majority of the votes is elected President. He or she does not have to be from the same political party as the members of the houses of Congress. The third branch is the judicial. Its members are chosen by the President and confirmed by the Senate. In the case of the US Supreme Court, the members are appointed for as long as they live or until they resign. They could possibly be removed for misconduct, but this has not yet happened in our history. I hope that clears up any confusion.