Barack Obama is leading John McCain in three key battleground states, a Quinnipiac University poll showed Wednesday.

Pennsylvania, Ohio and Florida are all potential swing states. Obama leads anywhere from 4 to 12 points in the polls taken June 9-16. At least two of the states are critical. Though Obama's campaign suggested earlier this week that it is not looking to concentrate on Florida or Ohio, Florida was the key state for President Bush's win in 2000 and Ohio was credited with returning the president for a second term in 2004.

This is the first time Obama has led in all three states. No one has been elected president since 1960 without winning two of the three largest swing states in the Electoral College.

Various media and poll outlets list the most likely battleground states and their Electoral College votes as Florida (27), Pennsylvania (21), Ohio (20), Michigan (17), Georgia (15) , and Virginia (13). The candidates need 270 electoral votes to clinch the presidency.

According to the poll, the largest gap is in Pennsylvania, whose 1,511 likely voters preferred Obama to McCain, 50-42 percent. The margin of error is 2.5 percent.

In Ohio, the 1,396 likely voters with a margin of error of 2.6 percent gave Obama a 48-42 percent lead.

Florida's 1,453 likely voters also favor Obama, but with the smallest gap, 47-43 percent. The margin of error is 2.6 percent.

The poll shows Pennsylvania independents leaning toward Obama by 11 percentage points, specifically those naming the economy and Iraq as the top issue. Pennsylvania's white voters favor Obama, 47-44 percent.

Florida independents lean toward Obama by 10 points. Ohio is essential even among independents.

The poll shows McCain ahead with whites in Florida, 50-40 percent, and in Ohio 47-44 percent.

Black voters favor Obama in all three states, with support at 90 percent or above according to the poll.

Not only do independents in all three states oppose Clinton as the running mate, many say they are less likely to vote for him if she is on the ticket. In Ohio, Obama's support among independents drops by as much as 10 percentage points if she is on the ticket. Majorities in Pennsylvania and Florida also oppose the so-called dream ticket of Obama-Clinton.

"The people who really matter come November - independent voters - turn thumbs down on the idea. And, many say they are less likely to vote for him if he puts her on the ticket," assistant director of the Quinnipiac University Polling Institute Peter A. Brown said in a statement accompanying the poll.

Race and age of the candidates also play a factor.

"One in five voters say McCain's age is a reason to vote against him. But overwhelmingly they don't see Obama's race as a factor at all - indicating that Americans are either much less concerned with race, or just don't want to tell callers what they really think on the subject," said Brown. The 18-34 group shows a preference toward Obama, while older voters are more divided with neither candidate above 50 percent.

Supporters are almost evenly split across the three states about changing their minds. In Pennsylvania, about a quarter of each senator's supporters say they could change their minds before the November election. Slightly more McCain supporters say they may change their minds in Ohio with 24 percent versus the 18 percent for Obama. Seventy-nine percent have their minds made up in Florida and 19 percent of voters there say they might change their mind.

Regarding who is most electable today, June 2008 is the first month Obama leads McCain with 42 percent to McCain's 39 percent. McCain has tied or led Obama since October 2007 in this question.