Barack Obama had it half right when he said that the McCain campaign would focus on raising voters' fears about him.

He was wrong in saying that the chief point of attack would be that he "doesn't look like all those other presidents on dollar bills." He wishes that were it.

But McCain does need to raise fears about Obama - that is, play on voters' worries about electing a man they don't know who has only a few years of experience in federal office. (Indeed, Obama's only been in the Senate since 2005 - and he spent most of 2007 and 2008 running for president, paying almost no attention to his duties in the Senate - as witness his absentee record.)

These fears will focus on two key areas: the economy and national security.

McCain needs voters to hear repeatedly - from top economists and office-holders - that Obama's tax-hike plans spell economic doom. The campaign must explain that Obama is not simply raising taxes on the rich - that he's crippling their ability to generate jobs, make investments and produce wealth. (For example: "When Obama says he'll only tax the rich, he's saying he will only tax the engine room, not the rest of the ship.")

The public must learn what the impact of doubling the tax on capital gains would be - how it would drive investment out of the country and cost us one to two points a year in economic growth for the rest of the decade.

Voters must hear how Obama can't possibly finance his programs - particularly his health-insurance schemes - with the tax hikes he's advocating. They need to ponder the impact of these tax hikes on an already slowing economy - it's legitimate to fear a new depression, not just a recession.

Economics is a field voters don't know much about and, consequently, fear greatly. Obama can capitalize on the current hard times - but he can lose big time if the impact of his tax policies is explained.

On national security, events could take over and put the issue center stage. But McCain must lay the groundwork to take advantage of whatever situation develops. He needs to hammer home the accusation that Obama is "naive" and "inexperienced" - both of which are obviously true. He should run ads mocking Obama's claim that Iran is a "tiny nation" that could pose no real threat to the United States. He needs to hit hard at Obama's plans for Iraq and Afghanistan, hammer at Obama's opposition to the surge and refusal to vote to pay for the troops.

The offshore-drilling issue helps McCain, but it doesn't conjure the kind of fear that national security and the economy do. McCain has a long task ahead of him of burying Obama's credibility on these issues, and he needs to begin right away.

For better or worse, this election is about Obama. It is a referendum on the Democratic candidate and his agenda of change. McCain is a well-known commodity: Voter opinions of him are not likely to change much in the next three months. But their view of Obama is subject to wild fluctuation.

That's why the undecided vote right now is running at twice its 2004 percentage at this time in the race. That's why older women are withholding their approval of Obama. McCain can and must use August to tilt these doubts into negatives.

It's starting to look like McCain can win - if he does the right things.