Obama is holding rallies in Denver and Fort Collins on Sunday.
McCain made three stops in Colorado on Friday, and both candidates' running mates have made recent visits, too.
Traditionally, Colorado has gone for Republicans in presidential races.
More broadly, Obama is using his record-breaking fundraising advantage to buy up media time and make what he hopes is a closing argument for the presidency. McCain and his team say the race is hardly over, particularly for a candidate who's had his share of comebacks.
Obama released a new TV ad Sunday that describes McCain as Obama often does on the campaign trail - as "out of ideas, out of touch and running out of time" and as resorting to smears and scare tactics because he doesn't have a plan to turn around the economy.
Obama's campaign said the 30-second ad will begin running on national cable television outlets on Monday.
Election Day is nine days away, on Nov. 4.
Confident and leading in most polls, Obama keeps playing on traditionally Republican turf. He is spending the diminishing campaign time in places that Bush won four years ago.
Obama on Saturday took shots at McCain's attempt to keep some distance between himself and Bush, a Republican presiding at a time when most people think the country is badly off track. The White House announced this week that Bush has already cast his vote for McCain.
"That's no surprise, because when it comes to the policies that matter for middle class families, there's not an inch of daylight between George Bush and John McCain," Obama said.
While Obama keeps up that theme, McCain is hammering a message that Obama is a tax-and-spend threat to the nation. Politically, the tanking economy has swung momentum in Obama's favor, but McCain is trying to win some back by casting aspersions about Obama's fiscal discipline.
Bush, meanwhile, has been quietly on the sidelines for virtually the entire election. But his name is mentioned often.
Other battleground states - Ohio, Pennsylvania, Virginia and Florida - are on Obama's itinerary as the final full week of the campaigning begins. McCain begins Sunday in Iowa and Ohio.