Because the most of the Republican candidates are making it very easy for her to get voters on her side. People like Trump, Christie, Huckabee, Santorum are going to kill the Republicans unless the party actually proposes policies that are consistent in the defense of liberty.
Another reason is simply that Democrats know she can win. I know a good amount of Dems who dont know sh** about Hillary's policies but support her because they know she can beat just about anybody the GOP can produce to go up against her
@Imabench, Good point and it touches on name recognition. If you have a candidate that has almost 100 percent name recognition, it's practically like that candidate is an incumbent president, which as we all know is very hard to beat.
I would say "because she has a vagina" but I believe it is a lot more complicated that. She just has more public appeal, most of which she received while her husband was in office, during the 2008 election, and relationship with current President Barack Obama. To say that she is only popular because she has a vagina would not be very honest, even if her being a woman helps her chances.
Their really isn't anyone on the Democratic side that is competing with her right now. Everyone nows she is going to get the nomination. The same can't be said for the GOP. A divided party can't compete with a unified one, regardless of which party it is.
Sanders is running on an open socialist platform, something that has been akin to political suicide in the past. He scares people. Their is no possible way he will get even a single members of the right to support him and even a large portion of the independents will be put off by his radicalism. Id say he has the least likely chance on the Democratic side of actually winning a national election.
Middle class American largely support him, due the the fact he is fighting for healthcare for all, and raising the minimum wage. He wants to get us out of the middle-east, which is probably a good thing.
Except that the middle class doesn't. The "middle class" has traditionally been split relatively evenly on the political spectrum, but in recent elections have been making more movements toward the right. The last congressional election is a symbol of that. In fact despite the demographics that the Democrats have increased by (minority votes and the poor), their has been a decline in the number of white middle class Americans supporting the party. As I said, Sanders is too radical for even moderates to be comfortable with.