WASHINGTON -- Hillary Rodham Clinton's campaign compared rival Sen. Barack Obama to the Clintons' chief nemesis of the 1990s, escalating their war of words since the former first lady won three primaries this week. Both campaigns on Thursday also announced huge gains in fund-raising ahead of what is turning into a long campaign. Clinton's campaign said she had raised $4 million online since Tuesday's wins in Ohio, Texas and Rhode Island. Obama's campaign countered by announcing he had raised a record $55 million in February, eclipsing the impressive $35 million that Clinton had raised then.

Clinton's victories has given her campaign new life, but her task remains daunting. Even if she wins every remaining contest, she cannot surpass Obama's tally of delegates won in primaries and caucuses. But Obama also cannot reach the 2,025 delegates needed for the nomination without the help of "superdelegates," the party and elected officials who automatically attend the convention and can support whomever they choose.

As of Thursday evening, Obama had 1,569 delegates and Clinton had 1,462. There were still 12 more delegates to be awarded from Tuesday -- 10 in Texas and two in Ohio.

With the next major opportunity on April 22 in Pennsylvania, both candidates are stepping up efforts to win over superdelegates to determine who goes up against Republican John McCain in the November U.S. presidential election.

Based on their current delegate counts, neither candidate can win enough delegates in the remaining primaries and caucuses to secure the nomination without the help of nearly 800 superdelegates.

Clinton, echoed by officials in Florida and Michigan, has renewed her call for new contests to be held in those states after they were stripped of their delegates by the Democratic Party for moving up their primaries ahead of schedule.

While Clinton won the popular vote in both states, none of the Democratic candidates campaigned there and Obama was not even on the Michigan ballot. But do-over contests in the two states, assuming Clinton wins again, could add some delegates to her total.

Meanwhile, the results were still pending from the second part of Texas' contest, the Tuesday night caucuses. Clinton beat Obama in the first step of Texas' contest, a standard state-run primary. But by Thursday, fewer than half of Texas' voting sites had reported results from the Tuesday night caucuses, the second stage of the state's primary.

Obama was leading in the caucuses by 56 percent to Clinton's 44 percent, but that was with only 41 percent of the precincts reporting.

Meanwhile, the two campaigns sought to score points against each other Thursday, and Clinton spokesman Howard Wolfson drew parallels between Obama and Kenneth Starr, one the of Democrats' greatest nemesis. Wolfson said Obama's statement that he plans to be more critical of Clinton's record is reminiscent of the attacks the Clintons endured during the investigations in the 1990s.

"Our point here is to point out that after a campaign in which many of the questions that voters had in the closing days centered on concerns that they had over his state of preparedness to be commander in chief and steward of the economy, he has chosen instead of addressing those issues to attack Senator Clinton," Wolfson told reporters in a conference call Thursday. "They've announced that this is what they are going to do.

"I for one do not believe that imitating Ken Starr is the way to win a Democratic primary election for president. But perhaps that theory will be tested," he said.

Many Democrats feel the Starr investigation was politically motivated, and injecting Starr into the debate is one more way for Clinton to depict herself as a victim of enemies out to get her. She has already complained recently about the media being against her.

Obama was not asked about Wolfson's comments during a television interview Thursday with ABC News, but he seemed to attribute his losses in three of four primaries this week -- after winning 11 in a row -- to a desire by voters to test him a little bit more.

"At a certain point, I think that people started saying, 'Well, maybe we wanted this thing to continue a little further,"' Obama said. "They want me to earn this thing, and not feel as if I'm just sliding into it."

On Wednesday, Obama told reporters he plans to increase his criticism of Clinton's record.

His campaign also has been attacking her for refusing to release her tax returns. The Clinton campaign said all the Clintons' returns since they left the White House will be made public around April 15 -- the deadline for filing U.S. income tax returns.

Obama spokesman Bill Burton said the comparison to Starr is "absurd" when Clinton has been calling for more scrutiny of Obama's record.

"We don't believe that expecting candidates for the presidency to disclose their tax returns somehow constitutes Ken Starr tactics, but the kind of transparency and accountability that Americans are looking for and that's been missing in Washington for far too long," Burton said in a statement.

"And if Senator Clinton doesn't think that the Republicans will ask these very same questions, then she's not as ready to go toe-to-toe with John McCain as she claims."

Meanwhile, Clinton was campaigning Thursday night in Mississippi, one of two smaller contests coming up this month.

Obama is expected to win Mississippi, which has 33 delegates, as well as a smaller contest Saturday in Wyoming, where 12 delegates are at stake in caucuses. But Clinton is competing in both states to hold down Obama's delegate accumulation.

Her appearance Thursday at a state Democratic dinner in Canton, Mississippi, and at a scheduled town hall Friday morning in Hattiesburg, could be her only stops in the Southern state.

"I'm well aware that Senator Obama has an enormous amount of support here, as he should, as he should have," Clinton said. "Some people have said 'Well Mississippi is very much a state that will most likely be in favor of Senator Obama.' I said 'Well, that's fine,' but I want people in Mississippi to know I'm for you."

In the Republican camp, McCain -- who surpassed the 1,191 delegates needed to clinch the nomination by sweeping the four contests that same night -- savored the moment after receiving President George W. Bush's endorsement.

McCain, who is 71, has said his foremost concern is finding someone capable of serving as vice president. But on Thursday, the veteran senator sidestepped questions about a choice.

"You know, obviously, we have just begun that process, and we, in fact, have not even outlined how we're going to go about this," McCain said at a news conference after he and Florida Gov. Charlie Crist shook hands with people at a local diner. "We're looking at how the process was conducted by other candidates and nominees of their party."

Crist has been cited as a possible running mate for McCain and the former Vietnam prisoner of war sang his praises, saying he was a "great governor" and that "there are many ways for him to serve the country."