(CNN) -- If polls were right early in the 2008 primaries, former New York Mayor Rudy Giuliani would have sailed on to become the Republican nominee for president.
That clearly didn't happen.
Texas Gov. Rick Perry jumped into the Republican race two weeks ago well after most of the field and surged past the other contenders in a Gallup Poll released Wednesday. Perry has the backing of 29% of Republicans or Republican-leaning independents, followed by former Massachusetts Gov. Mitt Romney at 17%, Rep. Ron Paul of Texas at 13% and Rep. Michele Bachmann of Minnesota at 10%. But that doesn't mean much this early in the race.
Between now and the first voting early next year, campaigns will rise and fall on their strategy and events beyond their control. Candidates' standings could look very different than they do now.
Former Sen. Fred Thompson of Tennessee got into the 2008 Republican primary race relatively late, announcing his candidacy on "The Tonight Show" in early September 2007. The politician-turned-actor-turned-politician saw a surge in a Gallup Poll taken September 7-12 when 22% of Republicans and Republican-leaning independents said Thompson was their choice. Giuliani was first with 34% of the vote.
The eventual GOP nominee, Sen. John McCain, was a distant third with 15%.
Thompson was criticized for being a "lazy" candidate who "didn't have his heart" in the race. The same cannot be said for Perry, who jumped into the race with both cowboy boot-clad feet and has campaigned relentlessly in the key early voting states of Iowa, New Hampshire and South Carolina.
Thompson's poll numbers fell and he was out of the race before the first month of primaries and caucuses was over in January.
Giuliani's lead fizzled because he pretty much chose to ignore early voting states and concentrate all his energy on the Florida primary. But that made the Florida vote make-or-break for Giuliani and when he finished third there, he was out of the race.
Retired Army Gen. Wesley Clark jumped into the 2004 Democratic race later than most of his rivals, announcing his candidacy in September 2003. Shortly after, he had a nearly 10-point lead in polls. A Gallup Poll conducted September 19-21, 2003, showed Clark (22%) leading the field of 10 Democrats, which included Howard Dean (13%) and John Kerry (11%).
At the time, Gallup offered this analysis: "The key question for Clark would be whether he can sustain this momentum. Polls conducted throughout the year have showed similar bounces for candidates just after they formally announced their intentions to run, but these increases have been short-lived. And as this suggests, much can change between now and the first crucial contests in Iowa and New Hampshire next January."
They were right. Clark's campaign fizzled by early February and Kerry went on to be the nominee.