Hillary Clinton and Barack Obama are preparing for a bitter battle to the end, after Clinton's three-state victory Tuesday kept her alive and virtually ensured the race will drag on through the Pennsylvania primary in April and beyond.

But the prolonged calendar has left both GOP and Democratic strategists wondering how to use the remaining primary schedule to make sure their party is victorious in November.

John McCain stands to gain considerably from a protracted Democratic race. Having clinched the Republican nomination, he is positioned to wage war on the Democrats as they wage war on each other. Conservative talk show hosts are already salivating at the prospect of Obama and Clinton bloodying each other, exposing each other's weaknesses and forestalling their own general election battle.

"(McCain) can save up some money while they spend their money attacking each other," talk show host Laura Ingraham told FOX News. "That's a win-win for Republicans."

Larry Sabato, director of the University of Virginia Center for Politics, said Clinton's victories Tuesday promised a drag-out fight.

"It didn't change the order of likelihood in getting the nomination," he said. "But what it did do is guarantee that we're going all the way through Puerto Rico in the first week of June."

Early signs from the candidates do not portend a pretty finale to the Democratic contest, which could threaten party unity post-convention.

"I'm concerned about unity. That's the major reason I've stayed out of this," said Sen. Bob Casey of Pennsylvania, who is neutral. "The longer this campaign goes on, the more difficult it will be to unify and heal."

Obama vowed to step his race up a notch Wednesday, after blaming his losses in Texas, Ohio and Rhode Island in part on negative campaigning. He said he planned to do more in the days ahead to raise doubts about his opponent's claims to foreign policy and other Washington experience.

"There's no doubt that Senator Clinton went very negative over the last week," he told reporters. "The kitchen sink strategy I'm sure had some impact, particularly in a contest when many of you in the press corps had been persuaded that you had been too hard on her and too soft on me."

Clinton consistently argued that Obama was not given due media scrutiny and in recent days tried to play up a Saturday Night Live sketch that suggested this. She also released critical ads, one of which asked voters who they wanted "answering the phone" in a crisis. It may have given her a boost -- late deciders trended more toward the New York senator Tuesday, FOX News exit polls showed.

The next contest is the March 8 Wyoming caucuses, followed by the March 11 Mississippi primary. Pennsylvania follows on April 22.

Obama's campaign immediately delivered on his pledge to criticize Clinton. Aides distributed a memo and held a conference call to question why she won't release her tax returns.

Obama adviser David Axelrod said, "This is not a decision to go negative. This is an attempt to see to it that both campaigns are held to the same yardstick, and it was the Clinton campaign who talked about the importance of vetting."

The Clinton campaign responded with a statement e-mailed to reporters while they were on the Obama call that said the Clintons' returns since they left the White House will be made public around April 15. And it countered, calling on Obama to release all information regarding his relationship with Chicago donor Tony Rezko, who is on trial for political corruption.

As the battle continues, Democrats are trying to suggest they will emerge unified at the end of the process.

"As we head towards November, our nominee must have the united support of a strong Democratic Party that's ready to fight and ready to beat John McCain. After seven years of Republican rule, I am confident that we will elect a Democratic president who will fight for America's families in the White House," Democratic National Committee Howard Dean said in a statement.

And while McCain could benefit from prolonged Democratic infighting, he could face negative repercussions as well.

Not only will he likely cede Page 1 media attention to the Democrats for what could be several months, but the attention he does get may be increasingly focused on his alignment with President Bush.

Bush endorsed McCain Wednesday, and McCain said he hopes Bush will make time in his schedule to campaign for him.

The Campaign to Defend America, a liberal special interest group, released a new ad Wednesday trying to cast Bush and McCain as clones.

"A trillion dollars in Iraq over the next 10 years. McSame as Bush. A millionaire who's for tax cuts for millionaires. McSame as Bush," says the ad's announcer.

The ad is among the first to be offered by liberal-leaning groups working independently of but in sympathy with  Democrats. According to FEC reports and filings with the Internal Revenue Service, the Campaign to Defend America is closely tied to the Fund for America, a nonprofit group set up last year by John Podesta, a former chief of staff for President Clinton; Anna Burger, the secretary-treasurer of the Service Employees International Union; and Rob McKay, a California philanthropist. The group has gotten millions in funding from liberal financier George Soros.

McCain's campaign appeared non-plussed by the expected onslaught.

"These groups spent tens of millions of dollars in 2004 against President Bush and he won re-election," McCain spokeswoman Jill Hazelbaker said. "It didn't work then and it won't work now."

Meanwhile, the Democrats are each trying to argue he or she is most likely to beat McCain when the general election finally does come around. A Clinton campaign memo Wednesday argued that the race is still close, and that Clinton is the most likely to defeat McCain in the general election. The campaign claimed McCain would eat into the independent base that has helped Obama in previous contests.

Clinton too said her resume is better suited to challenge McCain.

"Obviously Senator McCain will be a formidable opponent and he will, you know, bring quite extensive national security credentials.  He'll put his lifetime of experience up for the voters.  I'll put my lifetime of experience up for the voters.  And I think that, you know, voters were concerned what Senator Obama would put up, and therefore decided that, you know, I would be the person that would be, you know, the better commander in chief," she told FOX News.

The latest Gallup Democratic national tracking poll, taken from March 2-4, showed Clinton taking the lead in her primary race for the first time since Feb. 20, 48 percent to Obama's 44 percent. Clinton strategist Mark Penn pointed to the new poll as a "a very significant indicator that the string of states he won may in fact not be the best indicator of who would be the most electable candidate for this party."

But Obama had won 12 straight contests before Clinton swept the remaining three states Tuesday. The Illinois senator went into Tuesday's contests with a lead of 110 delegates, and the latest Associated Press delegate tallies show him leading by slightly fewer -- 1,567 to Clinton's 1,462 delegates.

He told FOX News on Wednesday that he's ready for the general election.

"John McCain has now consolidated the Republican Party behind his candidacy.  We're anxious to pivot to November where we can starting having a debate about which direction we need to move the country," he said.

Still, a winner must be decreed by activists in the Democratic Party. Clinton strategist Harold Ickes said he thinks the roughly 350 superdelegates who have not yet endorsed a candidate will now stay on the sidelines and watch the race play out to the end.

"We just think the superdelegates are keeping their powder dry, watching the process unfold. Three months to go before Puerto Rico finalizes the process and they're watching and waiting," he said.

FOX News' Aaron Bruns and Bonney Kapp and The Associated Press contributed to this report.