After Sen. John McCain swept all four primaries Tuesday, he feinted a reporter's question on campaign strategy by replying, "I've got to savor the moment."

He shouldn't savor it too long.

The Republican presidential nominee now has to fight even harder. Remember Rudy Giuliani? Political observers thought he was a cinch for the GOP nomination, but he was done in by his campaign's switches in strategy and a failure to effectively define himself amid the gaggle of early Republican candidates.

That's what McCain has to do -- especially now. He has to stay in the news. He has to stay relevant and squarely in the public eye. He shouldn't just pull up a chair and watch Sens. Hillary Clinton and Barack Obama duke it out for the Democratic nomination. He has to unmistakably distance himself from the Democrats.

Just as importantly, McCain has to distance himself from President Bush and the failed policies of his administration. He paid Bush a visit Wednesday for lunch and a formal endorsement.

While it's admirable and honorable that the former Navy officer isn't running away from his commander in chief, such moves make it that much more difficult for McCain to make that necessary separation. Obama is making it harder still by publicly painting McCain as Bush's identical twin when it comes to policymaking.

McCain must not let that campaign-stump rhetoric stand. He has to show without wavering that he grasps the important issues and how to properly address them. He has to show that he gets it on the illegal immigration issue. He has to show that he gets it on spending -- and the record bears out that he does. Wherever the Bush administration has come up short, McCain has to be right there with the correct solution.

McCain rightly reflected that in his acceptance speech Tuesday night. "Our campaign must be, and will be, more than another tired debate of false promises, empty sound-bites or useless arguments from the past that address not a single American's concerns for their family's security," he said.

"Presidential candidates are judged on their records, their character and the whole of their life experiences. But we are also expected to concentrate our efforts on the challenges that will confront America on our watch and explain how we intend to address them."

All that begins anew today, along with McCain's new mission to define himself.