(CNN) -- New Jersey Gov. Chris Christie's political troubles may reshape the Republican race much more radically than most commentators are yet predicting. To understand why, think of the Republican presidential nomination as a playoff game between two rival leagues. One league is composed of the Republican party's donors and professionals. The other features the party's activists and militants. In 2012, Mitt Romney triumphed early and totally in League A, and then waited patiently for the nomination as League B stumbled its way through a garish series of impossible candidates. The only plausible player fielded by League B, Texas Gov. Rick Perry, whiffled out before he had properly started the game.
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David Frum: Chris Christie, the leader among moderates, may not be a 2016 GOP contender
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Lack of a clear favorite may open way for GOP activists to pick the nominee, he says
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Candidates such as Ted Cruz and Rand Paul look more plausible, Frum says
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Frum: Old rules about how GOP picks a candidate may be thrown aside
A better League B puts new pressure on League A -- at exactly the same time when @placeholder seems be sputtering in the way League B sputtered four years ago.