Editor's note: David Frum, a CNN contributor, is a contributing editor at The Daily Beast. He is the author of eight books, including a new novel, "Patriots," and a post-election e-book, "Why Romney Lost." Frum was a special assistant to President George W. Bush from 2001 to 2002.
(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.
This time, though, League B has attracted plausible talent. Whatever any detractor may say about Ted Cruz and Rand Paul, they are U.S. senators. They may be unelectable to the presidency, but they are not inherently unnominatable, in the way that Donald Trump and Herman Cain were unnominatable.
A better League B puts new pressure on League A -- at exactly the same time when League A seems be sputtering in the way League B sputtered four years ago.
League A's brightest prospect, Christie, looks likely to soon be benched by self-inflicted injuries. There is other talent in League A, of course.
If interested, former Florida Gov. Jeb Bush could sweep League A -- but almost one-third of the way through the political cycle, he has yet to indicate that he is interested. Wisconsin Gov. Scott Walker has fans in League A, as do Florida Sen. Marco Rubio and former vice presidential nominee Paul Ryan.
This abundance of choice suggests that in 2016, unlike 2012, the League A contest will extend for a long time. The League A contenders will have months to run negative ads against each other -- and to remind League B fans why they dislike each League A player: Rubio, for wishing to widen immigration; Ryan, for writing a budget that cut Medicare and Medicaid; Bush, for his last name.
The prospect of a long and bitter battle within League A -- conjoined to improvements in the seriousness and professionalism of League B -- calls into question many of the usual rules of Republican politics.
Old Rule: The winner of the Republican nomination this time is the guy who came second last time. That rule held in every open contest from Ronald Reagan (runner-up in 1976) to Mitt Romney (runner-up in 2008). Not this time: In 2016, for the first time since the 1960s, there is no Republican heir apparent.
Old Rule: The Big Money always wins. From the rejection of Hillary Clinton in 2008 all the way back to the defeat of Edmund Muskie in 1972, Democrats have often preferred insurgents over leadership favorites. Not so Republicans. 2012 spectacularly confirmed the power of the Republican Establishment. But in 2016, the rule is looking wobbly for the first time since 1964.
Old Rule: Electability matters most in Republican presidential primaries. Tea party voters took chances in 2010 and 2012 on many oddball candidates for House and Senate. They played it safe at the presidential level. But many will feel that the defeat of McCain in 2008 and Romney in 2012 discredit the case for the "responsible choice." In 2016, Republican primary voters will for the first time since Barry Goldwater be offered a brace of seemingly plausible, irresponsible choices.
If League A looks as disorganized in 18 months as it does today, will the GOP's primary voters continue to refuse temptation?
The opinions expressed in this commentary are solely those of David Frum.