President Obama is promising a more aggressive approach in his debate next week with Mitt Romney and is offering some clues about how he intends to blunt his Republican rival’s momentum and reassure jittery Democratic supporters.

The president and his proxies have rolled out a sharper-edged message in the week since his lackluster first debate, hammering Romney over his changing positions on such central issues as tax cuts, health care and education.

The Democratic argument has been that Romney lied about his plans on the stage last week in front of 68 million television viewers in a way that disguises their potential impact on middle-class families.

In recent campaign advertising and in the president’s post-debate stump speeches, the outlines of Obama’s new approach are visible — and appear to reflect the lines of argument and rebuttal that he failed to make onstage in Denver. The strategy may become even more visible Thursday night, when Vice President Biden debates Republican vice-presidential nominee Paul Ryan in their only face-to-face encounter.

Obama has tested some catchy phrases in recent days. “That’s not leadership — that’s salesmanship,” the president said of Romney at a Tuesday campaign rally at Ohio State University, employing the kind of one-liner that his advisers had dismissed as un-presidential before the first debate.

In a radio interview Wednesday, Obama said he had been “too polite” onstage last week with Romney. It was the latest of several defenses the campaign has offered up since his performance in Denver; earlier, aides had said Obama was simply too stunned by Romney’s deceit to reply adequately.

Either way, Obama vowed to respond more energetically at their next matchup, at Hofstra University in New York on Tuesday.

“It’s fair to say we will see a little more activity at the next” debate, Obama said on the “The Tom Joyner Morning Show,” a nationally syndicated radio program. “We have four weeks left in this election, and we’re going to take it to them and make sure everyone understands what’s at stake.”

Romney advisers have called Obama’s questions about their candidate’s honesty evidence that the president is unable to defend his record on job creation, health care and the management of the deficit. Romney has sought to press his post-debate advantage in recent days, even taking on Obama’s foreign policy record, once seen as the incumbent’s strength.

In the radio interview, Obama said he expected the race to turn back his way, beginning Thursday night with the vice-presidential debate. He also dismissed the Democratic angst that has followed his performance in Denver as the same misplaced doubts that dogged his campaign four years ago.

“By next week, I think a lot of the hand-wringing will be complete because we’re going to go ahead and win this thing,” Obama said. “You were around in 2008. How many times were people saying we weren’t going to win?”

In a separate interview with ABC News’s Diane Sawyer on Wednesday, Obama said of the debate: “Governor Romney had a good night.  I had a bad night. It’s not the first time I’ve had a bad night.”

But he denied the debate might have handed the election to his rival. “What’s important is the fundamentals of what this race is about haven’t changed,” Obama said, according to a transcript released by ABC News. “You know, Governor Romney went to a lot of trouble to try to hide what his positions are.”

Polls tighten

Since the debate, the Democratic mood has darkened, with a marked tightening in national and swing-state opinion polls that has thrown the election into question with less than a month to go.

Worried supporters are hoping Biden, an experienced debater, delivers a well-argued defense of the administration’s record and a pointed critique of the Romney-Ryan candidacy that Obama largely failed to do last week.

“They had a strategy last time — a failed strategy,” former Pennsylvania governor Ed Rendell (D) said of the Obama campaign, whose advisers counseled the president not to be overly aggressive, for fear of looking petty onstage. “They changed strategies. But if I were advising them, I’d say don’t just turn this into a negative campaign. Talk about what you’ve done and your plans for the future.”

Obama will travel to Williamsburg, Va., on Saturday for three days of preparation with the same team that advised him last week, including Sen. John F. Kerry (D-Mass.), who has played Romney in mock debates with Obama; White House adviser David Plouffe; campaign adviser David Axelrod; and communications consultants Anita Dunn and Ron Klain.

Campaign officials have been largely silent on specifics of the preparation and Obama’s intent. But since the debate in Denver, the president and his proxies have offered a road map for what new to expect.

On Wednesday, Obama deputy campaign manager Stephanie Cutter and Planned Parenthood President Cecile Richards blasted Romney for seeming to back away from his anti-abortion position by suggesting in an interview with the Des Moines Register that he would not actively pursue legislation that would outlaw abortions.

The conference call underscored the Obama campaign’s concern over its lost edge with female voters, a once-sizable advantage that has largely evaporated since the Denver debate.

“With 26 days to go, he’s trying to soften his image,” Cutter said, referring to Romney. “We’re going to hold him accountable.”

Swing-state blitz

During visits to four swing states, including two visits to Ohio, after the last debate, Obama has sought to make the case that Romney misled viewers last week.

In addition, the Obama campaign and an auxiliary super PAC have reinforced the message with specific critiques of Romney’s debate statements in those states, plus several others now more in play after Obama’s performance in Denver.

Three days after the debate, the Obama campaign began broadcasting an ad called “Dishonest” in Colorado, Florida, Iowa, North Carolina, New Hampshire, Nevada, Ohio and Virginia. The spot focuses on Romney’s debate contention that he does not have a $5 trillion tax-cut plan, something Obama has said he has been campaigning on for months.

“If we can’t trust him to be honest now, how can we trust him in the White House?” the ad asks.

On Tuesday, the campaign released another ad in swing states that accuses Romney of repeatedly raising nursing-home fees during his tenure as Massachusetts governor and threatening Medicaid, an important way middle-class families pay to place elderly parents in nursing homes.

“We have a president who won’t let that happen,” the ad notes.

Priorities USA, the super PAC supporting Obama’s reelection, has echoed the danger-to-the-middle-class message as part of a $30 million advertising blitz in the final month before the election.

In an ad running in a half-dozen swing states, the group argues that Romney intends to cut public school funding to pay for tax cuts for the wealthy, ending with the line: “If Mitt Romney wins, the middle class loses.”

Neera Tanden, president for the liberal Center for American Progress, acknowledged that the race is tightening. But she said Obama has plenty of time to regain control if he is more willing to confront Romney directly about his changing positions.

“The president has an obligation not to be aggressive, but to say with a smile and point out to the American people that when a candidate says ‘A’ six months ago and ‘Z’ a month before the election, is he going to say ‘M’ when he’s president?” Tanden said.

For his part, Obama is projecting an air of confidence, making reference during the radio interview to an Internet meme featuring his photo with a superimposed slogan.

“As some of those e-mails going around with my picture on it say, ‘I got this,’ ” the president said.