Ready for Iowa? GOP race could take a turn

Grab your popcorn. Republicans are in for an interesting few weeks. With the Iowa caucuses coming up on Feb. 1, political prognostication is in full force. It's not unusual to hear dramatic statements across cable television outlets such as, "Jeb is finished!" "Name one state in which Marco Rubio can win?" or "How does Chris Christie go south?" But, such blanket statements fail to account for recent presidential primary history.

Nationally, in 2008, for example, a month before voting began, former New York City Mayor Rudy Giuliani was leading the Republican field. In Iowa, Mitt Romney led most of 2007, only to be overtaken by former Governor Mike Huckabee in December (The caucuses were Jan. 3 that year). At one point, shortly before Iowa voting occurred, Romney returned to the top of the polling charts, only to be overtaken once again by Governor Huckabee, who won the caucus vote. In New Hampshire, Senator John McCain also overtook Romney, who had led much of the race (and who some argued underperformed in the Iowa caucuses).

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Donald Trump and Jeb Bush speaking during the Republican Presidential Debate, hosted by CNN, at The Venetian Las Vegas on December 15, 2015 in Las Vegas, Nevada.

Romney never really recovered after Iowa. McCain, who performed poorly in most early state polling and was written off by most prognosticators, began to gain traction in New Hampshire in mid December. He doubled his Iowa polling position in the final two-and-half weeks before the Iowa caucuses and went on to tie late Senator Fred Thompson for third place. John McCain won the expectations game and he later won the New Hampshire primary. The rest is history.

In the 2012 race, at this point nationally, Newt Gingrich was leading the polls. If you were watching the Iowa caucuses three weeks before voting began in '12, you'd probably have bet on the former House speaker. He was atop the polls at 31 percent. He dropped precipitously as Ron Paul eventually took the lead only to be overtaken by a Romney surge. Worth recalling, former Pennsylvania Senator Rick Santorum tied Romney for the Iowa win. He outperformed his final polling average (16 percent) by 9 points. He and Romney both received just under 25 percent of the actual caucus vote.

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New Hampshire was less interesting in 2012. Mitt Romney led the race the entire time, pulling nearly 40 percent of the actual vote. 2012 was considered, overall, a weak field. 2016 is considered a strong field, with many capable political leaders stepping up to serve.

So, what does this tell us? With just over three weeks to go, lots can and will change. Just because someone has led much of the race, doesn't mean that's who will finish on top. Yes, it's hard to compare this field to any previous and Donald Trump has proven to be more than a novelty. But, history suggests it's more likely than not that there will be significant change in the polls over the coming weeks.

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It's possible Donald Trump stays atop the New Hampshire field as Mitt Romney did in 2012, but it's much more likely that whoever wins the expectations game in Iowa will get a bump in New Hampshire. That person will likely eventually be the one who challenges Donald Trump to be the GOP nominee.

Commentary by Sara Taylor Fagen, a partner at DDC Advocacy and a former Political Director for President George W. Bush. She is also a CNBC contributor. Follow her on Twitter @sarafagen2.

Follow CNBC's Opinion section on Twitter @CNBCopinion.

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