(Image Credit: Christopher Gregory/AP Photo)

Latinos, the nation's fastest-growing voting bloc, are poised to play a potentially decisive role in this fall's presidential election, but new data suggests that turnout might fall short of lofty projections, which could change the fate of the race for the White House.

The number of registered Latino voters has dropped significantly in recent years, from 11.6 million in 2008 to 10.9 million in 2010, according to new data from the U.S. Census Bureau's Current Population Survey. While 2008 was a presidential election year and 2010 was only a midterm congressional election, that is still a sizable decline, especially given the increase in the Latino population nationwide.

In the past decade alone, the Latino population has increased by 43 percent. There are more than 50 million Latinos in this country, nearly one in six Americans. A record 12.2 million Latinos are set to vote in November, a 26 percent increase from 2008, according to projections released in the fall by the National Association of Latino Elected and Appointed Officials (NALEO).

But that was before the new Census numbers revealed the surprisingly steep decline in registered Hispanic voters.

The William C. Velasquez Institute (WCVI), a non-partisan organization focused on Latinos' political and economic participation, crunched the Census numbers earlier this month and found that "a significant decline in national Latino voter registration in 2010 may diminish the size of Latino voter turnout in November 2012 by more than a million votes," according to the organization's president, Antonio Gonzalez.

The off-year decline in Latino voter registration is not unexpected: Registration fell by 4,000 voters after the 2004 presidential election. What is unexpected is that the drop in registration after the 2008 election was far bigger, a fall-off of 626,000 voters, down 5 percent. Nine states "experienced significant declines" in Latino voter registration in 2009-2010, WCVI found: California, Texas, Nevada, Florida, Washington, New Mexico, Michigan, New Jersey and Pennsylvania.

Some possible reasons for this decline, the group stated, are "a spike in residential mobility" coupled with "intensive downward economic mobility due to the combined effect of significant (and disproportionate) unemployment and mortgage foreclosures" in these nine states in the past two years. In January, for instance, a survey by the Pew Hispanic Center found that a majority of Latinos believed that the country's economic downturn had hit their ethnic group harder than other Americans.

The Velasquez Institute predicts now that national Latino turnout this fall will be "no higher than 10.5 million votes cast."

While Latino voter turnout might not appear crucial at first glance, it could potentially determine the fate of November's election, and who occupies the Oval Office for the next four years. Latinos cast 6.6 million votes in 2008 and, with more than two-thirds for President Obama, paving the way for the Illinois Democrat's resounding win. Generally speaking, Latinos are liberals, tending to disagree with Republicans on key issues such as immigration reform and the government's role in improving the economy. For Obama, Latino turnout could be the difference between winning and losing the White House.

The Obama campaign has made a concerted effort this year to replicate its success among Latinos four years ago. Campaign strategists frequently cite the growing Latino electorate as an advantage and they have taken aim at states with booming Latino populations such as Arizona and Colorado. To that end, the Obama campaign has pounced on some of the inflammatory rhetoric that Republican presidential hopefuls such as Mitt Romney and Rick Santorum have used toward Latinos in the past year's GOP primary.

For instance, after Romney vowed to veto the DREAM Act - the Democrats' measure to provide a path to citizenship for some children of undocumented immigrants who attend college or serve in the military - praised Arizona's strict immigration law that ordered immigrants to carry their registration documents at all times and mandated that police question them if there was reason to suspect that they were in the country illegally, and touted the endorsement of the controversial law's author Kansas Secretary of State Kris Kobach, Obama campaign surrogates dubbed Romney "the most extreme presidential candidate" ever on Latino issues.

Thus far, it appears, Chicago's strategy of ripping Romney's record with Latinos has worked. A late January poll conducted by Latino Decisions for ABC News and Univision found that 67 percent of Latinos would back Obama in a matchup against Romney, who only earned 25 percent of their support. Forty-one percent of Latinos nationwide said they had a somewhat unfavorable or very unfavorable view of Romney, while a whopping 72 percent of Latinos said the Republican candidates in the primary either didn't care too much about Latinos or were being outright hostile toward them.

But in what might be an alarming sign of lower-than-expected turnout this year, four in 10 Latinos nationwide said they were either not following the GOP primary too closely or not following it at all. In addition, a Pew Hispanic Center study released in December showed that a majority of Latino voters - 56 percent - have not yet engaged in the presidential campaign, saying they have given little or no thought to the candidates in the race.

Perhaps wary of that fact, Hispanic groups have kicked off efforts to increase the number of Latino voters come November. The National Council of La Raza has launched a national "Mobilize to Vote" campaign focused on registering and mobilizing thousands of Latinos, especially in critical swing states such as Florida, Nevada and Colorado.

The race is a close one in Florida, with Obama leading Romney 49 percent to 42 percent, according to a new Quinnipiac University poll released Wednesday. The Latino Decisions poll in January found a similar edge for Obama: 50 percent to 40 percent. But on the economy - the top issue for voters - Romney, who won the state's January primary, holds the edge on who would do a better job improving the country's fortunes: 48 percent for the former Massachusetts governor compared with 45 percent for the president, according to the Quinnipiac survey.

In battleground states such as Florida, both parties are well aware, Latino voters could swing the election one way or another, but only if they show up to vote. And that, it seems, is a real question at this point.

Matthew Jaffe is covering the 2012 campaign for ABC News and Univision.