The Gauntlet Has Been Thrown.

From PowerLine

Although there's no reason to doubt that Obama would fare well enough in a series of debates with McCain, Obama is unlikely to accept McCain's challenge. This is standard practice for non-challengers, but normally the non-challenger is an incumbent president or a sitting vice president. Voters are sufficiently familiar with such candidates to decide a "referendum" without seeing the candidate debate his opponent more than once in the fall (the non-challenger normally agrees to a few debates as a safety net in the event the first debate goes badly).

This is not the case with Obama, though. Voters will not easily decide to crown Obama without reasonably frequent exposure to him in pressure situations. Sound bites and soaring but largely vacuous speeches will not do the trick; Obama needs to begin facing McCain and taking questions from the public, not just listening to its hard luck stories. If he seems to be ducking this completely or to a significant degree, the advantage will go to McCain.