Barack Obama’s 30-minute campaign commercial Wednesday night was not merely a tactical decision to carpet-bomb millions of Americans in pursuit of a few thousand undecided voters who can dictate the outcome of the presidential campaign.

Aired on seven network and cable stations, the ad served as a national get-out-the-vote organizing tool for Obama operatives. It offered even the swiftest channel-flipper the chance to see Obama looking presidential, helping to condition voters to that possibility. And once again it proved to John McCain, and everyone else, how Obama’s deep pool of campaign cash has allowed him to rewrite the rules of presidential campaigning.

As the years-long pursuit entered its final days, Obama’s commercials were pelting important electoral states, trying to smother efforts by McCain to diminish Obama’s lead in polls of voters nationally and in most key states.

According to an accounting by the Neilsen television research company, Obama was running more than twice as many ads across the country as McCain, even after the Republican increased his television buys.

The closing days of national campaigns are usually an exercise in frustrating choices, with decisions made over which dollars can be spared for a host of competing needs. Even if a campaign decides it should make a move, financial constraints can make it impossible to pull off. Because of its wealth, Obama’s campaign has faced that dilemma less often.

That meant it was more than twice as easy to hear Obama’s message as McCain’s.

“At some point, the tonnage of Obama commercials makes it difficult for McCain to get his message out,” said Ken Goldstein, a University of Wisconsin-Madison political scientist who studies political advertising.

The half-hour Obama ad was a classic closing commercial, with a positive tone that belied the hand-to-hand combat going on in key states, both on the air and on the ground. He did not mention the names of his opponents, nor was there more than an elliptical reference to President Bush.

Americans may be near the saturation point when it comes to the presidential race, but the stark reality for both candidates is that the days until Tuesday are running down, and with them options for changing the trajectory. One of the side benefits to Obama’s media splash Wednesday was that it overshadowed McCain on Wednesday, analysts said.

“It’s blocking out McCain,” Goldstein said. “It’s not so much about what (the ad) says good about Obama. John McCain has six days to disqualify Obama. It’s like the end of the football game, and Obama is running out the clock.”