Huckabee's announcement will have an immediate impact on the race. Most candidates decline to run because they know they have no chance of winning the nomination. Huckabee, on the other hand, had a clear path to victory through Iowa and South Carolina, where he was leading in the polls. Huckabee's departure will leave a vacuum that other candidates will race to fill, radically altering the shape of the race. The 2012 Republican primary will be quite different without Huckabee.
His decision does not affect all candidates equally. Elephant Watcher will recalculate the odds and issue a thorough explanation of the changes later. Generally speaking, candidates who rely on a victory in Iowa will benefit more than those relying on New Hampshire. Candidates with a higher chance of winning will tend to benefit more than obscure ones, since most voters gravitate toward prominent candidates.
Given Huckabee's strong position in the race, many political commentators will speculate about his reasons for not running. Huckabee's contract with Fox News gives him a financial incentive not to run, though one wonders why he did not spend the next few months continuing to milk the speculation about his intentions. Besides, a strong presidential run would only enhance Huckabee's stature and ability to earn money through paid speeches, books, etc.
It's quite common for family members to discourage candidates from running. In 1996, Colin Powell wanted to run for president, but his wife was adamantly opposed, fearing he would be assassinated as Martin Luther King, Jr. was. Scandals can also play a role, as in 2008, when Al Gore's infidelity prevented him from making a run. Of course, some candidates run regardless of scandals, as both Hillary Clinton and John Edwards did in 2008. In Huckabee's case, there is no indication that scandals are a factor.
During his announcement during his TV show, Huckabee said that his family was fully supportive of him making a run, and the polls were in his favor. Huckabee said that his decision not to run came during spiritual deliberations that he cannot fully explain.
Unless Huckabee can elaborate further, his motives will remain a mystery. In any case, the 2012 Republican primary field has begun to take shape. Over the next few weeks, it's likely several other potential candidates will make official announcements. The fact that Huckabee is out may make others more inclined to run.