Republican presidential nominee Senator John McCain(L) and his wife Cindy wave to the crowd at the end of a campaign rally in Wallingford, Pennsylvania November 2, 2008.[Brian Snyder/Reuters]

Opinion polls show McCain is struggling to defend about a dozen states won by Republican President George W. Bush in 2004.

McCain's prime hope of a breakthrough in a Democratic-leaning state is Pennsylvania.

Obama has led in every opinion poll in the state this month, although his edge has narrowed from double digits, to between 4 and 7 points.

McCain trails Obama in every national opinion poll and in many crucial battleground states ahead of Tuesday's vote, but aides say he is closing the gap at the end of a campaign that has lasted nearly two years.

A Reuters/C-SPAN/Zogby poll on Sunday puts Obama's national lead at 6 percentage points.

Other recent national polls put the advantage for Obama at between 4 and 13 points, with the race holding steady.

(CCTV November 4, 2008)