2016 GOP race wide open

New Jersey Gov. Chris Christie has fallen out of the top spot among potential Republican presidential candidates with a political scandal roiling his administration.

Hillary Clinton continues to have an overwhelming lead over other possible 2016 Democratic presidential candidates. Although the former first lady and secretary of state has not said whether she'll run, a group of PACs and advocacy organizations have begun the process of raising money and aiding a hypothetical campaign.

Vice President Joe Biden has twice before made unsuccessful bids for the Oval Office -- in 1988 and 2008. A former senator known for his foreign policy and national security expertise, Biden made the rounds on the morning shows recently and said he thinks he'd "make a good President."

Sen. Marco Rubio, a Republican rising star from Florida, was swept into office in 2010 on the back of tea party fervor. But his support of comprehensive immigration reform, which passed the Senate but has stalled in the House, has led some in his party to sour on his prospects.

Rep. Paul Ryan, a former 2012 vice presidential candidate and fiscally conservative budget hawk, says he's "keeping my options open" for a possible presidential run but is not focused on it.

Sen. Rand Paul said last March that he was seriously considering a run for president in 2016. If the tea party favorite decides to jump in, he likely will have to address previous controversies that include comments on civil rights, a plagiarism allegation, and his assertion the top NSA official lied to Congress about surveillance.

Texas Sen. Ted Cruz plans to travel to states that factor into the early nomination process. The first-term Republican and tea party darling is considered a gifted orator and smart politician. He is best known in the Senate for his marathon filibuster over defunding Obamacare.

Maryland Democratic Gov. Martin O'Malley released a "buzzy" political video in November 2013 in tandem with visits to New Hampshire. He also headlined a Democratic Party event in South Carolina, which holds the first southern primary.

Republican Texas Gov. Rick Perry announced in 2013 that he would not be seeking re-election, leading to speculation he might mount a second White House bid.

Louisiana Gov. Bobby Jindal said recently it's too early to announce whether he'll run. Jindal has said he wants to focus on "winning the war of ideas" before making a decision on his presidential ambitions.

Former Pennsylvania Sen. Rick Santorum, a social conservative, gave Mitt Romney his toughest challenge in the nomination fight last time out and has made trips recently to early voting states, including Iowa and South Carolina.

Political observers expect New York Gov. Andrew Cuomo to yield to Hillary Clinton should she run in 2016, fearing there wouldn't be room in the race for two Democrats from the Empire State. Should she not jump in, Cuomo would then be a potential candidate.

Gov. Scott Walker of Wisconsin is considered a possible Republican candidate, but he recently told CNN that his priority is to first help the GOP capture the Senate in next November's midterms.

Former Florida Gov. Jeb Bush has said his decision to run for the Republican nomination will be based on two things -- his family and whether he can lift America's spirit. His father and brother formerly served as President.

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• David Frum: Chris Christie, the leader among moderates, may not be a 2016 GOP contender


• Lack of a clear favorite may open way for GOP activists to pick the nominee, he says


• Candidates such as Ted Cruz and Rand Paul look more plausible, Frum says


• Frum: Old rules about how GOP picks a candidate may be thrown aside

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.

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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?

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The opinions expressed in this commentary are solely those of David Frum.