The prospect for an even longer Democratic battle resulted from Clinton's defeat of Obama in Pennsylvania on Tuesday, meaning the contest is likely to last at least another two weeks until May 6, when North Carolina and Indiana vote.
As top McCain adviser Mark Salter said, Democrats should "take their time -- don't rush."
Republican strategists believe McCain has benefited from having won his party's nomination in March, giving him time to raise much-needed cash and lay the groundwork for his general election campaign, even though the Democratic battle has dominated U.S. headlines.
The Clinton-Obama battle has meant the Democrats have not yet trained all their fire on McCain, a 71-year-old Arizona senator who is seeking to keep the White House in Republican control for a third straight term, a task made even more difficult with the U.S. economy ailing.
"During this period the Democrat interest groups have not been able to focus on McCain," said Republican strategist Scott Reed. "They're still focused on struggling with their internal fight."
McCain himself sounded unsure as to whether the long Democratic fight has helped or hurt him, but in talking to reporters on Tuesday, he made clear he has been watching the show closely.
"In fact I saw one of the cable shows last night -- I don't know why I watch! -- that said that this is really good for the Democratic Party, that they are registering more voters, that it's getting more interest, that they're raising more money. I don't have a view on that. But I know that there are very different opinions on it," he said.
Recent financial reports show McCain trails both Democrats in raising money.
McCain said he was "absolutely neutral" in the Democratic race. "I have never stated whether I wanted this election to stretch out or not. That's up to Democratic Party voters, and I have nothing to do with it."
Still, McCain has been training heavy fire on Obama, who many pundits believe will ultimately win the Democratic contest.
McCain criticized Obama's talk of raising the capital gains tax on stock profits, basically accusing him of inexperience.
"That's out of touch with America's economy and it's a fundamental misunderstanding of the basics of economics," McCain said.
McCain advisers have prepared plans to campaign against either of the Democrats. Senior adviser Charlie Black has looked at each Democrat and concluded that either would be tough opponents.
"I don't see one as easier than the other," he said.
Black said Obama has charisma and has brought new voters into the process, while Clinton has a smart, sophisticated, "ruthless bunch of people" with battle-hardened campaign experience.
"There's no substituting for experience," he said.
Salter said each Democrat offers a different set of challenges, that some states are in play if it is Obama and vice versa with Clinton.
Said another adviser, Steve Schmidt: "We are ready for the race no matter who the opponent will be. Both of them are good and it will be a very close contest all the way to the end."
Pennsylvania Sen. Arlen Specter, speaking to Fox News Channel on Tuesday, said he believes Obama will ultimately represent the Democrats against McCain and sees good and bad for McCain.
"When Obama and McCain stand up side-by-side, there's going to be an enormous contrast, some positive and some negative: positive for McCain on his experience, positive for Obama on his youth and his promise for the future," he said.