where the two options most Americans are realistically considering are "my ideal candidate on the left" and "Democrats"?
Political Left: Nader has a following. Sanders (votes with Dems mostly) has a following. Obama has a following (primarily Democrats).
Political Right: Ron Paul has a following. Barr has a following. McCain has a following (primarily Republicans).
Most people pick one (your choice), and understand that most American voters support Democrats or Republicans. Neither party (and certainly not a third party) can win without picking up some of his/her opponent's base.
American politics is complicated: Sen. James Inhofe (Kook-OK) doesn't believe in global warming and he voted against the bailout. From
Think Progress:
Inhofe’s office has said he “does not hire openly gay staffers ‘due to the possibility of a conflict of agenda.’” Standing before a large photograph of his family on the Senate floor in 2006, Inhofe proudly declared that “in the recorded history of our family, we’ve never had a divorce or any kind of homosexual relationship.”
Yet the people of Oklahoma continue returning this nut to the Senate.
On edit: I remember the debate after the 2006 election. Some claimed centrist won the day. Others noticed a
shift to the left. One thing is certain, progress doesn't happen overnight.
edited for clarity.