I have been around politicians for a good part of my life and I have found that it takes a special person to run as the "sacrificial lamb" against a seemingly unassailable opponent. They need to be charismatic enough to mobilize their base and to help people farther down the ticket. They also need to be strong enough personally to know that--in spite of what they say during the campaign--they are not going to win. The general public will not thank them for their work. They are seen as delusional or quixotic. However, many people involved in politics themselves are grateful and they may be appointed to something. Also their profile may be raised in a way that helps them in the future (either politically or professionally). Even in the worse case, it is something that they can always say they did. In fact, I have known some people who have represented the Democratic Party in elections for purely altruistic reasons, feeling that a differing and minority view needed voice and representation. There may very well be Republicans as well, but I do not know them personally, that's all.
Every once in a while, though, they have the chance to win. For example, Scott Brown probably thought he would be running against Deval Patrick right about now. Sure, ask him and he will say that he was running to become "the next Senator from Massachusetts" or "to restore American values in Washington" or some such thing. But really, the opportunity fell in his lap and he took it.
Thanks to recent Tea-Party victories we can see a similar situation in the Great State of Alaska. Delaware, the home of oddball Christine O'Donnell, doesn't count because Democrat Chris Coons stood a reasonable (but not overwhelming) chance of winning anyway. This is not the case in the Land of the Midnight Sun, but things will still have to fall his way for sacrificial candidate Scott McAdams to become its next senator.
You see, the Murkowski write-in cuts both ways. If Joe Miller was even a little more normal, then Dems would feel comfortable going for McAdams. However, it looks like many will be going with the "dark-horse incumbent" to stave off disaster. I have been watching this contest from the other side of our great nation and I do think McAdams has a chance. He seems fairly charismatic and thoughtful ("amiable" is what the national press calls him, though they sometimes don't mention him by name) but right now he is in a stiff fight for second. Still, there is always hope. This campaign season is nuts. Perhaps he can find a way to impress enough moderates and independents to squeeze ahead.
As I implied earlier, the nation press likes to see this as a Miller v. Murkowski "soul of the GOP" smackdown so it is hard to learn much about McAdams. I am not so sure that the rather simplistic trend in journalism is a good thing..so here is his webpage.