Is this the end of the trail?

Heading into a potentially decisive round of contests today, Hillary Rodham Clinton stayed on the attack against rival Barack Obama on Monday, trying to turn around a campaign that has been battered by 11 straight defeats.

Many political observers -- including Clinton’s husband, the former president -- have said she needs strong victories in delegate-rich Texas and Ohio to remain a serious challenger for the Democratic presidential nomination. Those contests have overshadowed the primaries also taking place today in Rhode Island and Vermont.

Still, in a campaign season highlighted by its unpredictability, other political analysts say that if neither Clinton nor Obama scores a pair of solid wins in Texas and Ohio, the battle might continue on to the April 22 Pennsylvania primary -- or even beyond.

Clinton herself suggested Monday that she planned to press ahead. “I’m just getting warmed up,” she said at a news conference here. Political analysts said a surprising double loss for Clinton in the two big states today, however, would almost certainly doom the candidacy of the one-time front-runner.

“If she loses both states, nobody is going to believe any spin” that there is life left in the Clinton campaign, said Donnie Fowler, a Democratic strategist who was Al Gore’s national field director when Gore ran for president in 2000.

“Her own surrogates, including her husband, have set the bar pretty high, but pretty clear for her,” Fowler added. “She probably needs to win both Ohio and Texas, and she certainly needs to win one of those states.”

Gale Kaufman, a Democratic political consultant who worked on Bill Bradley’s 2000 campaign for the presidency, agreed that Clinton needed clear triumphs in Texas and Ohio to overcome her opponent’s momentum and catch up in the delegate count.

If Clinton falls short of that, Kaufman said, “it’s hard for the Obama campaign not to have the upper hand at that point and not to say: ‘Look, the math doesn’t work. We have seven weeks before the next major primary; that’s time that really could be used effectively to bring everyone together.’ ”

On the other hand, Kaufman said, if Clinton wins convincingly in Ohio, where the polls show her with a lead, and keeps the combined primary-caucus close in Texas, where surveys show the candidates neck and neck, “it’s going to be really difficult for her to feel like she should get out.”

Clinton can make a case, Kaufman said, that she has fared well in most of the biggest states and she should hang on until Pennsylvania.

But Kaufman called that “a longshot strategy” that would spur grumbling among Democratic activists.

Clinton campaign officials, and the New York senator herself in a day of campaigning in Ohio and Texas, launched blistering attacks Monday against Obama.

The main accusation was that an Obama advisor gave private assurances to Canadian officials that the candidate’s criticism of the North American Free Trade Agreement -- which was highlighted in last week’s Ohio debate between the candidates -- was only political posturing.

During the debate, both candidates pledged to renegotiate NAFTA, a signature accomplishment of Bill Clinton’s administration, to add environmental and labor protections. NAFTA has been blamed by critics for a huge loss of U.S. manufacturing jobs, and the Illinois senator has emphasized his concerns while campaigning in economically struggling Ohio.

But Clinton’s campaign, fanning a recent flap that it branded NAFTA-gate, cited a memo written by a Canadian official about a meeting between a senior Obama economic advisor, Austan Goolsbee, and Canadian consulate officials in Chicago.

The memo reassured Canadian government officials not to take Obama’s message “out of context” and to view it “as more about political positioning than a clear articulation of policy plans.”

Speaking to reporters at a Toledo hotel, Clinton criticized Obama, saying he was giving “speeches that are very critical of NAFTA, and you send out misleading and false information about my positions regarding NAFTA, and then we find out that your chief economic advisor has gone to a foreign government and basically done the old wink-wink -- ‘Don’t pay any attention, this is just political rhetoric.’ ”

Goolsbee, a University of Chicago economist, has disputed the assessment of the memo, as has the Obama campaign. The Canadian Embassy also weighed in Monday, saying that the report out of its Chicago consulate contained “no intention to convey, in any way, that Sen. Obama and his campaign team were taking a different position in public from views expressed in private, including about NAFTA.”

Clinton officials also raised questions about Obama’s ties to Chicago businessman Antoin “Tony” Rezko, whose trial on federal influence-peddling charges began Monday in Chicago. In a conference call with reporters, Clinton communications chief Howard Wolfson urged the Obama campaign to release all the documents it may have about Rezko.

The issues seized by the Clinton campaign put Obama in a rare defensive mode. After an afternoon town-hall meeting with veterans in San Antonio, Obama was pressed repeatedly by reporters about Goolsbee’s actions.

“Nobody reached out to the Canadians to try to reassure them about anything,” Obama responded. “They reached out -- unbeknownst to the rest of us -- they reached out to Mr. Goolsbee.”

Obama tried to turn the incident to his benefit, arguing that “this notion that Sen. Clinton is peddling that somehow there’s contradictions or winks and nods has been disputed by all the parties involved.”

What is not disputed, he told reporters, “is that Sen. Clinton and her husband championed NAFTA, worked on behalf of NAFTA, called it a victory, called it good for America until she started running for president.”

The Clinton campaign, Obama said, “has been true to its word in employing a kitchen sink strategy . . . three, four things a day. This is one of them. It doesn’t, I think, change the facts.”

Still, Obama spent critical time on an important campaign day explaining that the Canadian consulate in Chicago contacted Goolsbee in his position as an economics professor and offered him a tour, “and he went down as a courtesy.”

The conversation turned to trade and NAFTA, Obama said, “and the Canadian Embassy has confirmed that he said exactly what I’ve been saying on the campaign trail -- which is that I believe in trade, but that it is important for us to have labor standards, environmental standards that are enforceable, and that I intend to obtain modifications and amendments to NAFTA that will make them enforceable.”

At the San Antonio gathering, which had a heavy complement of reporters from Obama’s home base of Chicago, Obama challenged contentions that he had not revealed how often Rezko held fundraisers on his behalf.

Obama said there had been several hundred stories on the issue, “and the fact pattern remains unchanged.”

He said that Rezko was his friend and supporter, raised money for him and many other candidates of both parties, and was now on trial for charges that were “completely unrelated to me.”

“What is also true is that I entered into a real-estate transaction with him in which I bought a strip of land adjacent to a property that he had purchased,” Obama said. “And I have said that that was a mistake. There have been no allegations that I did anything wrong. There have been no allegations that I did him favors. We have disgorged all the money that we can identify that was raised by him.

“That is the extent of the story. I don’t excuse myself from having made an error.”

The presumptive Republican nominee for president, Arizona Sen. John McCain, pushed ahead Monday in his bid to close out the GOP race, which has become a sideshow to the Democratic contest despite its continuing primaries. Campaigning in Waco, Texas, he criticized both Clinton and Obama, accusing the Democrats of pandering to voters on NAFTA, and expressed his support for free trade.

“I believe NAFTA has been a great benefit to the state of Texas and this country,” McCain said. “I’m not going to go to Ohio and tell you I’m against it and then come to Texas and not say a word about it.”

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maria.laganga@latimes.com

louise.roug@latimes.com

stuart.silverstein@ latimes.com

LaGanga reported from Texas, Roug from Ohio and Texas, and Silverstein from Los Angeles. Times staff writer Maeve Reston also contributed from Texas.