...when candidates declare this early. The conventional wisdom is that they'll peak too early and be stale come election time.

Not that they've declared, but the fact that everybody assumes they'll run makes the declaration just a formality. People have been speculating about both of them for a long, long time...so long that in a sense it'll be a relief when they finally get it over with.

The bigger wildcard, I think, is internal party politics, and maybe that's what you have in mind. The RNC has already torpedoed McCain once, and it's anybody's guess whether they'll decide to put pragmatism over ideology to run an eminently electable candidate even if he is a "RINO".

As for Hillary, I doubt the DNC has the power to block her. That the Democrats are nowhere near as organized and disciplined as the Republicans is a distinctly mixed blessing for them. But a mirror dynamic may apply to Hillary: Where the Republicans hate moderates, Democrats will fret over the perception that Hillary is too Liberal. It may turn out, in fact, that Hillary's prospects of making it through the primaries depend on whether McCain runs too. They're a matched set; change one, and you have to change the other.

It's a horserace, and I'm looking forward to it.