The last week of the presidential campaign has been the nastiest to date, with outrage stoked, allegations leveled and apologies demanded.

Nothing new there. Campaigns are — in the modern era — races to the bottom, a lowest common denominator battle to slime the other guy before he slimes you. (USA! USA!)

What has changed is that it’s Democrats pushing the political envelope and Republicans insisting that a line has been crossed.

Former Massachusetts governor Mitt Romney said late Friday that the attacks by President Obama on his record at Bain Capital were “ridiculous and of course beneath the dignity of the presidency.” Matt Rhoades, Romney’s campaign manager, took it a step further, demanding that Obama apologize for the allegations — calling the charges “so over the top that it calls into question the integrity of their entire campaign.”

How did the Obama campaign respond? “

On Monday, Democratic National Committee Chairwoman Debbie Wasserman Schultz counseled the Romney campaign to “put their big boy and big girl pants on” and defend Romney’s record.

“Stop whining,” urged former White House chief of staff and current Chicago Mayor Rahm Emanuel. A new ad funded by Obama’s campaign, meanwhile, features Romney singing “America the Beautiful” while stats are shown on screen about outsourcing under Romney and his Swiss bank account — among other things.

The Obama response amounts to a collective sticking out of the tongue — or another gesture involving your hand — at the Romney campaign. What Obama’s campaign is saying with the level of rhetorical aggression — and the unapologetic reply to the controversy it has caused — is that it is willing to push the boundaries and do so unrepentantly.

During a campaign appearance in Cincinnati Monday, Obama continued his fussilade, suggesting that the former Massachusetts governor supports limited taxing of U.S. corporations abroad that would encourage more jobs to flow overseas.

“We have not found a serious economic study that says Gov. Romney’s economic plan would actually create jobs, until today, I have to be honest,” Obama said, citing a report by Tax Notes report. “Today we found out there is a new study by non-partisan economists that says Gov. Romney’s economic plan would in fact create 800,000 jobs. There’s only one problem. The jobs wouldn’t be in America.....We don’t need a president who plans to ship more jobs overseas,” Obama said.

The Obama campaign’s aggressive attacks show signs of working. Polls indicate that Romney's business experience was widely seen as a positive attribute early this year, but has taken a hit in swing states since attacks hit the airwaves. A June NBC/Wall Street Journal poll found Romney's business record drawing especially negative views in a broader swath of swing states, with 33 percent saying they feel “more negative” vs. 18 percent “more positive” toward Romney given what they’ve heard about his work “buying, restructuring and selling companies.” Nationally, the split was 23 percent positive to 28 negative on Romney's work.

Bain Capital has definitely gained some traction as a campaign issue in the last week. ABC’s Emily Friedman points out that “Bain Capital” was one of the top ten Google searches Monday morning, and a Google chart tracking search traffic for Bain Capital over the last 30 days shows that interest has increased dramatically since last week. Six of the 10 top states where interest in Bain stories is highest are swing states, The Atlantic points out.

The Romney campaign is clearly concerned about being on the defensive rather than the offensive.

In an interview on Fox News Monday, Romney asked "What does it say about a president whose record is so poor that all he can do in his campaign is attack me?" Romney asked. "A campaign based on falsehood and dishonesty does not have long legs.”

Romney signaled a coming shift from defense to offense, promising to scrutinize the president’s political donors and their impact on his agenda. "The best offense is to look at the president's record," Romney said.

The shoe has often been on the other foot.

Remember back to the 2004 presidential campaign where conservatives — led by Swift Boat Veterans for Truth — effectively undermined Sen. John Kerry’s (D) candidacy with a campaign that focused on attempting to discredit his military service in Vietnam.

Or to the 2002 Georgia Senate race when then Rep. Saxby Chambliss (R) ran ads featuring images of Sen. Max Cleland (D), a triple amputee, alongside those of Saddam Hussein and Osama bin Laden.

Or to 1988 when Republicans attacked Michael Dukakis (D) over a convicted felon named Willie Horton.

You get the idea. Democrats always felt as though they won the “moral” victory, but Republicans won the actual victory. (That reality has been a constant lament of Democratic strategists ever since we have been covering politics.)

Now, Democrats will insist that questioning Romney’s business ties is different than questioning the military service of Vietnam veterans. But line-crossing is often in the eye of the beholder, and the aggressiveness Obama and his team have adopted is more important than the actual issue on which they have decided to fight.

Obama, in an interview with CBS News’s Charlie Rose that aired Sunday, said he doesn’t blame Romney for attacking his economic record.

“That is his argument, and you don’t hear me complaining about that argument,” he said. “Because if I was in his shoes, I’d be making the same argument.”

Obama, of course, doesn’t want to start taking certain attacks off the table, given that Romney has cried foul over the Obama team’s use of his record at Bain Capital.

The reality is that 2012 may not be a campaign that Democrats will look back on lovingly — as they do when it comes to the 2008 campaign — but the incumbent seems to understand that winning, whether beautiful or ugly, is the ultimate goal.