Pres. Obama pitches in Colorado, Mitt Romney compares California's economy to Greece

The effort to cleave Obama from a popular policy of Clinton's presidency comes weeks before the former president is to be a marquee speaker at the Democratic National Convention. Gingrich — who pushed through the 1996 welfare bill and later led the charge to impeach Clinton — said he wanted to remind Americans "how much weaker and less effective a president Obama is than the man who is nominating him."

The welfare issue as pushed by the Romney campaign appeared to be aimed at blue-collar whites in a weak economy and suggested that Obama might be gaining ground politically with his position on taxes.

After the Des Moines appearance, Romney flew to New Jersey to raise money for his campaign. On his way to the airport, the former Massachusetts governor stopped at a corn field to talk with a farmer about the severe drought gripping much of the nation.

In Denver, Obama said women's health issues resonated with him because of his wife, Michelle, and his late mother. The president said he wanted to make sure his wife "has control over her health care choices." He also noted that his mother would have turned 70 this year had she not died from cancer nearly two decades ago.

"I often think about what might have happened if a doctor had caught her cancer sooner," Obama said.

Obama also highlighted his decision to appoint two women to the Supreme Court and said the next president "could tip the balance in a way that turns back the clock" for women in the next decade.

The president was introduced by Fluke, a Georgetown law student who gained notoriety after conservative talk-show host Rush Limbaugh called her a slut because she supports the Obama health care law's requirement that insurance companies cover contraception.

Fluke said when she was "verbally attacked" Obama "was one of us. He defended my right to speak without being attacked, and he condemned those hateful words." Recalling the incident, Fluke mocked Romney for saying at the time that Limbaugh's words "aren't the words I would have chosen."

"If Mr. Romney can't stand up to extreme voices in his own party, then he will never stand up for us," Fluke said.

With the trip to Denver, Obama opened a two-day, four-city swing through Colorado, focusing his events on the economy, including his call for Congress to extend tax cuts for families making less than $250,000 a year while letting the cuts for higher-income earners expire.

A new Quinnipiac University poll shows Obama and Romney tied among voters in Colorado households earning between $30,000 and $50,000 per year — an important target. Obama leads among voters with lower incomes; Romney is favored by those making more.