Barack Obama faced one of his toughest days on the campaign trail Monday, fending off a barrage of attacks from Hillary Clinton, whose camp vows she will fight on past Super Tuesday 2, regardless of the results.

Clinton campaign officials went on offense Monday on a number of issues, paying particular attention to national security and trade matters that are important to voters in Ohio and Texas, which hold primaries Tuesday along with Rhode Island and Vermont.

Clinton's camp lobbed last-minute grenades at Obama with a new ad that claims the Illinois senator was negligent in his oversight duties as chairman of a Senate Foreign Relations subcommittee. The ad claims he failed to conduct due diligence in monitoring the activities of European allies in the fight in Afghanistan, and therefore he cannot be trusted to manage national security.

The ad quotes Obama saying that he became chairman at the beginning of 2007, so it's true he hadn't yet held any oversight hearings. An announcer then says, "Hillary Clinton will never be too busy to defend our national security, bringing our troops home from Iraq and pursuing Al Qaeda in Afghanistan."

The ad comes on the heels of another released last week called "3 a.m.," which Clinton senior adviser Mark Penn called a "tipping point" that shifted momentum toward Clinton.

Penn did not offer any evidence to demonstrate that, but a study released Monday by the nonpartisan Center for Media and Public Affairs indicated that recent election news analysis of broadcast networks showed Obama's "good press" went from 5-to-1 positive to 2-to-1 positive. It also indicated that Clinton gets better coverage on discussions of her issue positions and performance in office.

Obama still gets ample coverage about his likability, but on Monday he spent a good part of his day fending off accusations about a meeting one of his senior economic policy advisers had with the Canadian consul general in Chicago. In that visit, adviser Austan Goolsbee suggested that the hard talk coming from the campaign over the North American Free Trade Agreement was just rhetoric.

The memo to Canadian officials at home by Consul General Joseph DeMora, which Goolsbee says misrepresented his remarks, was released to the public Monday. It read that Goolsbee "was frank in saying that the primary campaign has been necessarily domestically focused, particularly in the Midwest, and that much of the rhetoric that may be perceived to be protectionist is more reflective of political maneuvering than policy."

Speaking to reporters in Toledo, Clinton said the memo should leave voters wary of her opponent.

"If you come to Ohio, and you both give speeches that are very critical of NAFTA and you send out misleading and false information about my position regarding NAFTA, and then we find out that your chief economic adviser has gone to a foreign government basically, and done the old wink wink, don't pay any attention, this is just political rhetoric, I think that raises serious questions," she said, repeating her accusation that the media is playing softball with her opponent.

"I would ask you to look at this story, then substitute my name for Senator Obama's name and see what you would do with this story," she said.

On Monday, the Canadian Embassy released a statement saying that the report produced by the consulate general in no way intended to convey that Senator Obama and his campaign advisers "were taking a different position in public from views expressed in private, including about NAFTA. We deeply regret any inference that may have been drawn to that effect."

The embassy added that U.S. voters "are fortunate to have strong and impressive candidates from both political parties," and Canada "will not interfere in this electoral process."

Obama said that should be the end of the discussion, particularly since Goolsbee was speaking to the consul general without the knowledge of the campaign.

"This notion that Senator Clinton is peddling that somehow there is contradictions, or winks and nods, has been disputed by all the parties involved," Obama said. "What has not been disputed is that Senator Clinton and her husband championed NAFTA, worked on NAFTA, called it a victory, called it 'good for America' until she started running for president," he said. "I know the Clinton campaign has been true to its word in conducting a kitchen sink strategy."

Obama's surrogates also tried to defend the candidate on his national security credentials. Sen. John Kerry said the Clinton ad "does a disservice to the dialogue" on national security and "are the kind of ads you would expect Republicans to run."

Rep. Chet Edwards, D-Texas, said the "3 a.m." ad was one "Karl Rove would be proud of." Edwards said he expects Texas Democrats to reject the ads because they don't like ads that play on post-Sept. 11 fears.

"I don't think Texas Democrats are impressed by the politics of fear-mongering," he said. "Campaign commercials that Karl Rove could have written will not fly with Texas Democrats."

Kerry said Obama welcomes the national security debate because "it highlights Obama's judgment" on the Iraq war. He added that the scare tactic is a "phony issue" because Clinton has never had a to deal with a "3 a.m." crisis.

Kerry added that Clinton needs to win Ohio and Texas by a wide margin to carry forward her bid for the nomination credibly.

"I don't think it [is] sufficient to sneak by in Texas and Ohio," Kerry said.

Despite Obama's rough day, more and more Democrats are saying that if Clinton doesn't meet the standard established by her husband and advisers -- that she win both Ohio and Texas -- she will have a very hard time convincing the country generally, and Democratic voters and superdelegates, that she should carry on with her campaign.

The Clinton campaign acknowledged Monday that its earlier prediction that it will close the delegate gap between the New York senator and Obama will not stand. The best-case scenario is a narrow victory in Texas and a wider win in Ohio. With losses in Vermont or Rhode Island, the distribution of pledged delegates could become too overwhelming to surmount.

Even with victories, Clinton officials recognize she will be 100-160 pledged delegates behind Obama in the race to get to 2,025. Howard Wolfson, campaign communications director, said the campaign expects to "be successful" Tuesday but declined to establish a benchmark to measure success.

Wolfson said the campaign is likely "to enter an interesting phase" after Super Tuesday 2 with six weeks after the smaller Wyoming caucuses on March 8 and Mississippi primary on March 11 to explore and scrutinize Obama's record.

With that admission, Obama's camp is expecting to recover its footing quickly. Obama officials said the only question left for the Clinton campaign if it does not significantly erode Obama's lead on Tuesday is to determine what plausible path it has to even up the pledged delegate count in the remaining contests.

"There are 611 pledged delegates left after March 4th contests," said Obama campaign manager David Plouffe. "They would need to win at least 62 percent of all remaining pledged delegates to get back to even. ... If they do not win Texas and Ohio by healthy double-digit margins -- and they led by healthy double-digit margins as recently as two weeks ago -- they will be facing almost impossible odds to reverse the delegate math.

"While the Clintons gamely continue to try to move the goal posts, at some point there has to be a reckoning. It is a very simple question -- what is their path to secure the nomination? No amount of spin can change the math. We look forward to their tortured answers on Wednesday morning," Plouffe said.

FOX News' Major Garrett and Carl Cameron contributed to this report.