Hillary Clinton launched a new line of attack on Barack Obama on Monday, assailing his failure to vote up or down on the Senate's Iran resolution and slamming his penchant for skipping votes during his tenure in the Illinois Legislature.

Clinton said Obama's long-running criticism of Clinton's support for a get-tough Senate resolution on Iran lacks credibility because he skipped the vote entirely. Obama has called the vote a means to initiate a rush to war against Iran.

"If he really thought it was a rush to war, why did he rush to campaign and miss the vote?" Clinton asked, calling the skipped vote part of an Obama pattern of dodging important issues.

Clinton said lawmakers can vote yes, no or "present," a choice Obama has made "on issue after issue."

"It's kind of like voting maybe," Clinton said.

Clinton said Obama voted present seven times on abortion-related issues, and twice on gun violence and on issues relating to firearms near school grounds.

"A president can't vote present," Clinton said. "Instead of looking for political cover and taking a pass, we need a president who is willing to take a stand."

Both candidates were in Iowa Monday, where the first-in-the-nation caucuses are just one month away. Obama fired back at Clinton, characterizing her comments as "silly" and announcing the launch of a new web site his campaign has created to document and knock down all the attacks against him by Clinton's campaign.

"It's silly season," Obama said of Clinton's remarks. "I understand today she's been quoting my kindergarten in Indonesia."

Click here to view the Web site.

Clinton also repeated her criticism of Obama's health care plan and took a swipe at his plans to encourage out-of-state students who attend Iowa colleges and universities to caucus for him on Jan. 3.

Clinton said she was trying to mobilize "Iowa residents who live here and pay taxes." Iowans, as a rule, fiercely guard the pre-Iowa dimension of the caucuses. Howard Dean's efforts to mobilize out-of-state students who attended Iowa schools in 2004 backfired in that it generated more negative publicity than young caucus-goers.

Clinton's hardball tactics mark a new turn in the race after polling shows Obama making strong headway in the Hawkeye State. Instead of being cowed by the new polling, Clinton has come on strong, describing the month before voting begins for the Democratic presidential primary nomination as the "fun" part of the campaign.

Whether it's fun for the candidates remains to be seen, but Obama isn't taking the jabs lying down. Obama campaign spokesman Bill Burton also offered a strong counterargument Monday claiming Clinton is trying to distort Obama's voting record.

"Hillary Clinton's idea of fun continues today by attacking Barack Obama's 100 percent pro-choice rating and his record of leadership in reforming the death penalty, passing racial profiling legislation and enacting the first major ethics reform in 25 years," Obama campaign spokesman Bill Burton says on the site.

"The truth is, Barack Obama doesn't need lectures in political courage from someone who followed George Bush to war in Iraq, gave him the benefit of the doubt on Iran, supported NAFTA and opposed ethanol until she decided to run for president," Burton says.

The tit-for-tat comes after a harrowing day in which Clinton lambasted the Illinois senator for everything from a kindergarten essay to his health care plan and use of his political action committee to funds candidates in early primary states.

On Sunday, Clinton's campaign issued a memo suggesting that Obama is lying when he told voters in Boston that he has has "not been planning to run for president for however number of years some of the other candidates have been planning for," a seeming reference to Clinton.

Clinton responded by having her campaign issue a press release in which news articles show that Obama wrote in both kindergarten and third grade essays that when he grows up he wants to be "a president."

"I'm sure tomorrow they'll attack him for being a flip-flopper because he told his second grade teacher he wanted to be an astronaut," Burton said in response.

Back in Iowa, Clinton got down to the issues, declining to say if Obama has a character problem, but suggesting that he "skirted" Federal Election Campaign rules by using PAC money for candidates that could help him and by claiming to propose a health care plan that is not truly universal.

She added that with just a month until the first-in-the-nation caucuses in Iowa, she's ready to turn the tables on all the negative statements against her and spend the next month drawing greater contrasts between her and her Democratic rivals.

"I have said for months that I would much rather be attacking Republicans and attacking the problems of our country because ultimately that's what I want to do as president. But I have been, for months, on the receiving end of rather consistent attacks," Clinton said at a Cedar Rapids, Iowa, stop designed to encourage first-time caucus-goers to attend and vote for her.

"Well now the fun part starts. We're into the last month, and we're going to start drawing the contrasts. Because I want every Iowan to have accurate information when they make their decisions. I don't expect to get 100 percent of the vote. But I want people to know what they're voting for, and to make the contrast, to make an informed decision. So we're going to be out there telling the people of Iowa what the facts are, setting the record straight, and having a good time doing it," she said.

Obama then slammed Clinton for suggesting that the race is just about having fun.

"This presidential campaign isn't about attacking people for fun, it's about solving people's problems, like ending this war and creating a universal health care system. Washington insiders might think throwing mud is fun, but the American people are looking for leadership that can unite this country around a common purpose, and that's what I'll continue to offer in this campaign," he said.

Obama's aggressive responses to Clinton, compounded with suggestions that she is saying whatever she needs to get elected, has helped propel him to the top spot in Iowa, according to the latest Des Moines Register poll that puts Obama at 28 percent compared to Clinton's 25. John Edwards is trailing closely with 23 percent in the poll of 500 likely Democratic caucus-goers taken Nov. 25-28. The margin of error was 4.4 percent

But an AP-Pew poll out Monday of 460 likely Democratic voters gave Clinton 31 percent to Obama's 25 percent, within the 5.5 point margin of error.

Obama winning Iowa will help deny Clinton the sense of inevitability that she has been trying to build in voter's minds, but Clinton still has a strong national organization and could easily recover from a second place finish. An apparent dread for that outcome has launched even Republican strategist Karl Rove to get into the act.

Rove offered his unsolicited advice to Obama in a Financial Times "memo" to the candidate on how to beat Clinton.

In the article out Monday, Rove said it's imperative that Obama beat Clinton in Iowa if he wants to be taken seriously on a national level. He adds that he's done the smart thing by getting a strong organization up in Iowa, but Obama needs to add more vigor to his campaign.

Click here to read The Financial Times article.

"First, stop acting like a vitamin-deficient Adlai Stevenson. Striking a pose of being high-minded and too pure will not work. Americans want to see you scrapping and fighting for the job, not in a mean or ugly way but in a forceful and straightforward way," Rove wrote.

"Find a way to gently belittle her whenever she tries to use disagreements among Democrats as an excuse to complain about being picked on. The toughest candidate in the field should not be able to complain when others disagree with her. This is not a coronation. Democrats do not like her sense of entitlement. She is not owed the nomination. It does not belong to her simply because her name is Clinton. So blow the whistle on her when she tries to become a victim. Do it with humor and a smile and it will sting even more," he continued.

FOX News' Major Garrett contributed to this report.