Updated 7:02 p.m. ET

Mitt Romney slammed President Obama's tactics in a series of TV interviews tonight, charging his Democratic rival with launching attacks that are "beneath the dignity of the presidency and his campaign."

The presumptive GOP presidential nominee took the rare step of appearing on ABC, CBS, CNN, Fox News and NBC to discuss his work at Bain Capital, which has been a frequent topic for Obama and his campaign this week.

Romney's defense of his private-sector work -- as well as his criticisms of Obama's integrity -- are among his most extensive yet during this race.

BLOG: Obama says Bain questions 'legitimate'

Obama also took to the airwaves, telling WJLA-TV in Washington that Romney has a "responsibility" to provide more details about his years at Bain.

Romney told Carl Cameron of Fox News that the attacks from Obama have made politics "a lot worse than usual." He said people expected more from a man who talked in 2008 about wanting to be "post-partisan."

Yesterday, the rhetoric between the two presidential campaigns got particularly heated over Romney's tenure at Bain Capital, a private-equity firm.

Stories in Mother Jones and The Boston Globe, citing government documents and campaign filings, reported Romney was listed as Bain's CEO and sole owner from 1999 to 2002. Romney has said he left the company in February 1999 to run the 2002 Winter Olympics in Salt Lake City.

Bain was involved in a number of investments during those years in which companies either had to cut jobs, file for bankruptcy or move jobs overseas -- and Rommey's role in those investments is at issue.

Asked about Securities and Exchange Commission documents, Romney said this on CNN to reporter Jim Acosta:

There's nothing wrong with being associated with Bain Capital, of course. But the truth is that I left any role at Bain Capital in February of '99. ... I think anybody who knows that I was out full-time running the Olympics would understand that's where I was.

Obama told WJLA-TV that questions about Romney's work at Bain are "legitimate."

"If he aspires to being president, one of the things you learn is, you are ultimately responsible for the conduct of your operations," Obama said.

Romney also dismissed calls that he release more tax returns, saying on CNN that he will not disclose anything more than than his filings for 2010-2011. Earlier this year, he released his 2010 tax return and an estimate for 2011.

"Those are the two years that people are going to have. And that's all that's necessary for people to understand something about my finances," he said.

On ABC, Romney said Obama "sure as heck ought to say that he's sorry" for assertions made by his staff, including a suggestion by deputy campaign manager Stephanie Cutter, that the Republican may have committed a felony for misstatements to the SEC.

"The president needs to take control of these people," Romney told ABC's Jonathan Karl. "He ought to disavow it and rein in these people who are running out of control."

(Contributing: Jackie Kucinich and Cooper Allen)