Cain is polling at only 6 percent.
"Today, a campaign builds on itself," Brown says. "Typically fundraising follows credibility and credibility comes from experience and fundraising. There isn't a reshuffling that happens."
Historian Richard Norton Smith says another reason media often shape a race early on is that doing so creates a more intense and personal race for viewers to watch.
"A lot of people find it frustrating to try and follow eight or nine people on stage," he says. "Viewers want to see a race. They want to see something memorable like the Ford-Reagan race of 1976 or the Carter-Kennedy race of 1980. Those battles were epic and compelling, and media want to re-create that in a race for a nomination."