WASHINGTON (AP) — Hispanic Americans, the fastest growing minority group in the United States, favor President Barack Obama over presumptive Republican nominee Mitt Romney by a huge margin, a potentially decisive factor in the Nov. 6 election.

Hispanics are critical because of the complex state-by-state system for choosing the U.S. president.

They could tip the vote in the president’s favor in key swing states like Colorado, Nevada and Florida. What’s more, the Hispanic vote could put once-solidly Republican Arizona in play for Obama.

First Lady Michelle Obama was in Arizona on Monday, testing the waters for her husband at a fundraiser. She also stopped in three other heavily Hispanic states in the U.S. southwest — Colorado, Nevada and reliably Democratic New Mexico. Vice President Joe Biden also was in Arizona two weeks ago, courting voters who last settled on a Democrat for president when Bill Clinton won re-election in 1996.

Hispanic voters historically have sided with Democratic presidential candidates out of a sense that the party best handled the immigration issue, which tops their list of concerns. They appear to be sticking with Obama despite his record-setting deportation of illegal immigrants. The Department of Homeland Security shows that since 2009 the number of deportations has approached 400,000 each year, well above the number during the George W. Bush presidency.

In the latest poll by the Pew Research Center for the People & the Press, Obama overwhelms Romney by 67 percent to 27 percent among Hispanic registered voters. That support matches the 67 percent of the Hispanic vote Obama captured in 2008.

Romney has alienated many Hispanics with his support of Arizona’s tough new immigration law as “a model” for the nation. The initiative, approved in 2010, has been denounced by Hispanic and immigration rights groups as extreme. Challenges to the law recently were argued before the Supreme Court, where both liberal and conservative justices indicated they were not in favor of overturning the measure.

During Republican primary debates, Romney said that “the right course for America is to drop these lawsuits against Arizona. … I’ll also complete the (border) fence. I’ll make sure we have enough border patrol agents to secure the fence, and I’ll make sure we … require employers to check the documents of workers.”

Romney also opposes the Democrats’ Dream Act legislation that would allow a path to citizenship for the children of illegal immigrants if they serve in the military or go to college.

Romney’s positions put him to the right even of Republican opponents Rick Santorum and Newt Gingrich. He now faces the challenge of finding a way to shift toward the center if he is to have any hope with Hispanic voters.

Obama carried Colorado, Nevada and Florida in 2008, and keeping those states in his column could prove essential in this year’s voting. With six months remaining before the vote, national polls show the president and Romney in a very close race, with the struggling economy the top issue. That should be especially important to Hispanics, who have 11 percent unemployment while the overall jobless rate is 8.2 percent.

Perhaps the biggest question about Hispanic preferences arises in Florida, one that could prove key to the hopes of both candidates.

Mark Lopez of the Pew Hispanic center cites “changing demographics” there, which show more Hispanics registering as Democrats in the last two elections. In the past, the Florida Hispanic population had been dominated by Cubans, who are heavily Republican given that party’s history of a greater antagonism to Communist revolutionary leader Fidel Castro and his successor and brother, Raul.

But Puerto Ricans are a fast-growing part of the Hispanic community there and they overwhelmingly back Democrats.

In a hypothetical head-to-head general election matchup with Obama, 40 percent of Florida Hispanics said they would vote for Romney, while 50 percent prefer Obama, according to a Univision News/ABC News poll from late January.

The poll found that Florida Cubans side with Romney over Obama 54 percent to 34 percent, while Puerto Ricans back Obama 67 percent to 23 percent.

Nationally, if the election were held now, Obama would safely carry 14 traditionally Democratic states, mainly the East and West Coasts, and the District of Columbia, with a total of 186 electoral votes. Romney probably would prevail in 20 reliably Republican states, primarily in the South and West, worth 156.

Electoral votes in the end are more important than the popular vote. Democrat Al Gore won the popular vote in 2000 but lost the race to George W. Bush, who accumulated the most electoral votes. The election system really amounts to 50 separate state-by-state contests where the winner is awarded the number of electoral votes assigned to that state according to the number of representatives it has in the House of Representatives, plus the two senators each state has in the Senate.

The winning presidential candidate must triumph in enough states to accumulate 270 electoral votes, half plus one of the 538 total electors. The candidate who does best in Nevada, Colorado and Florida will have a significant advantage. That will especially be the case for Obama if he can add traditionally Republican-voting Arizona to his count.

Copyright 2012 The Associated Press.