The party affiliation does not mean a whole lot in USA; the district is a solidly conservative district. Social conservatism rules the day. Republicans had high hopes of winning it; they had invested lot of money and lot of resources into the election. It was a bitter disappointment for them not to win it.
Sure Paul is a Libertarian, he has said so himself (or at least he claims to be a Libertarian, some conservatives claim to be Libertarian rather than conservative, I suppose it sounds more respectable). However, now he is the Republican candidate and Republicans are stuck with all the baggage he carries.
And a senate election receives much more coverage than a house election (his father is a House member).
That is an internal matter for the Democratic Party, I doubt that the two candidates are that much different.
Elected Senate in USA is of relatively recent origin, initally Senators used to be elected by state legislatures.
I would not get to technical when you try to explain U.S. politics, much better to stay with generalities. I personally would not even attempt to understand Canadian or British politics, just make comments on end results. There is a reason why we tried to disassociate ourselves with your political structure, and we even had a civil war to refine ourselves even more. I am thankful the U.S. does not have a unelected second chamber. The U.S. 17th Amendment 4/8/1913 changed when Senators were elected by state legislatures and established direct election of United States Senators bypopular vote.
The Old Medic obviously knows what he is talking about in this instance. Another very good statement by him.