However, the population of uninsured Americans seemed to have little influence on the vote. According to data from the Census Bureau's 2008 American Community Survey, 101 congressmen from districts where the rate of the uninsured was above the national average voted against the bill. That's compared to only 96 representatives from districts with an uninsured population above the national average that voted for the bill. On the other side, 124 representatives from districts where less than the national average are uninsured voted for the bill compared to just 114 against.

Of the 193 districts that went to McCain, 175 voted against the bill, including 31 McCain districts represented by a Democrat. Fiscally conservative Democrats were also split on the bill: Among the centrist Blue Dogs, 27 voted for the bill and 24 voted against even after Speaker Nancy Pelosi, D-Calif., amended the public option portion to garner their votes.

Moderate Democrats were drawn to the bill after the passage of an amendment from Rep. Bart Stupak, D-Mich., which would bar federal funds from being used for abortions. Sixty-four Democrats joined Republicans in voting for the amendment, including Michael Michaud of Maine and John Salazar of Colorado, moderates who ended up voting for the final bill.

Cao, the lone Republican vote for the bill, helped Democrats overcome the loss of 39 party members and push the support over the 218-vote threshold. Cao's district, which went for Obama, has 21.7 percent of the population uninsured.

The historic vote marked the further progress for a health care reform bill, a staple of Obama's domestic agenda. Speaking after the vote, Pelosi said, “This legislation will mean affordability for the middle-class, security for our seniors, and honors our responsibility to our children, adding not one dime to the deficit.”