By JEFF ZELENY

With just weeks remaining in this long presidential race, Senator Barack Obama is going after Senator John Mc- Cain more aggressively than at any other point in the campaign, with a professorial tone giving way to one of prosecution.
“John McCain says he’s about change, too - except for economic policy, health care policy, tax policy, education policy, foreign policy and Karl Rove-style politics,” Mr. Obama, the Democratic nominee, told his supporters in Virginia on September 9. “That’s just calling the same thing something different.”
These days, he sounds more like the sharp-tongued commercials seen on television.
“Do you really believe John McCain is going to make a difference now-” said Mr. Obama, mentioning his Republican rival’s name twice in the same breath, a pattern he repeated again and again. “John McCain doesn’t get it.”
Obama offered a blistering critique of Republican handling of the economy on Monday, September 15. Over the weekend, the prominent securities firm Lehman Brothers had filed for bankruptcy protection and the investment bank Merrill Lynch was acquired by Bank of America. The Dow Jones industrial average dropped 500 points by the end of the day.
“The fundamentals of our economy are strong,” Mr. McCain said that day at a rally in Florida. “But these are very, very difficult times.”
Mr. Obama pounced on the remark. “We just woke up to news of financial disaster this morning and he said that the fundamentals of the economy are still strong?” Mr. Obama told voters at an afternoon rally in Colorado. “Senator McCain, what economy are you talking about?”
He added, “Senator McCain - you can’t run away from your words and you can’t run away from your record. When it comes to this economy, you’ve stood firmly with George Bush and a failed economic theory, and what you’re offering the American people is more of the same.”
Mr. Obama’s advisers said that combative edge was essential to blunt any progress Mr. McCain was making as he sought to encroach on Mr. Obama’s trademark message of change. Or perhaps it is in response to cries of alarm from Democrats who believe he is being too mild-mannered.
But Mr. Obama’s remarks are curiously reminiscent - right down to that mocking tone - of words he spoke nearly a year ago when Senator Hillary Rodham Clinton suddenly tried to swipe the mantle of change and Mr. Obama demonstrated a fight that many Democrats had doubted he could muster.
Mr. Obama has been in this place before: finding the proper temperature to aggressively critique - or attack - his rival without tarnishing his own image of trying to remain above traditional politics. As he enters the final eight weeks of the race, advisers said, the lessons from the Democratic primaries are alive in his head.
Mr. McCain and his running mate, Governor Sarah Palin, seem to be there, too.
“A month ago, they were all saying, ‘Oh, it’s experience, experience, experience,’ ” Mr. Obama said, speaking over booming applause recently in a high school gymnasium. “Then they chose Palin and they started talking about change, change, change.
What happened- What happened- What happened?”
For one of the few times in his presidential candidacy, Mr. Obama is suddenly not the freshest and most telegenic figure on the ballot. While he seems to have settled on a line of attack against Mr. McCain, his campaign appearances since Ms. Palin joined the Republican ticket make clear that he is still grappling with his approach to her.
He has declared her family off limits. He has praised her biography, telling an audience, “Mother, governor, moose shooter - that’s cool.” But he has taken sharp aim at her record as Alaska governor.
There were plentiful signs in recent days that the voters turning out to see Mr. Obama liked his forceful tone, with several audiences chanting along with him, “Eight is enough! Eight is enough!” which has become a rallying cry for changing Washington after eight years of the Bush Administration.
His presence and energy on stage resembled how he began to act last fall as his extended primary battle with Mrs. Clinton became fully engaged.
But as in his primary battle with Mrs. Clinton, Mr. Obama’s new aggressive posture comes with possible pitfalls - real or created by the opposition - as he again navigates the tricky terrain of gender politics.