Democrat Barack Obama leads Republican John McCain in six of eight key battleground states one day before the U.S. election, [ including the big prizes of Florida and Ohio ], [ according to a series of Reuters/Zogby polls [ released on Monday ] ]. Obama holds a 7-point edge over McCain among likely U.S. voters in a separate Reuters/C-SPAN/Zogby national [ tracking ] poll, up 1 percentage point from Sunday. The telephone poll has a margin of error of 2.9 percentage points. Obama heads into Tuesday's voting in a comfortable position, with [ McCain struggling [ to overtake Obama's lead in every national opinion poll ] and [ to hold off his challenge in about a dozen states [ won by President George W. Bush in 2004 ] ].