The challenge to McCain will be considerable: get past the very attractive Obama packaging and get voters to focus on what Obama is actually proposing (e.g. withdrawal from Iraq, end of the Bush tax cuts).
But at the moment, what Obama is "actually proposing," on Iraq and taxes alike, is considerably more popular with voters than what McCain is proposing. According to this month-old poll, 74 percent of Americans don't want "large numbers of U.S. troops" in Iraq for more than two years; 50 percent want to be out within a year. Or again, here's a December poll in which 56 percent say that victory in Iraq is no longer possible, and 57 percent say that we should withdraw "most troops" by 2009. This is good news for Obama, bad news for McCain. And the same goes for the Bush tax cuts. As of this October, 61 percent of Americans either wanted them repealed outright, or agreed that "tax cuts for the wealthy should be repealed, while others stay in place" - which is precisely what Obama is promising.
Now obviously future developments in Iraq could alter these dynamics, and so could the way that McCain and Obama go about debating the issues come the fall - and how the press ends up framing their positions. But at the moment, I think the GOP might have at least much luck going after Obama's "packaging," which is ideal for a Democratic primary but possibly less so in a general election, as they would going after him on taxes and Iraq. (Do Americans really want to put a "world man" in the Oval Office? Do they really want to pick a President based on his potential appeal to young Pakistani Muslims? Do they really want to vote for a guy whose campaign has become a vehicle for an "indie-yuppie political fantasy"? etc.) And I'm nearly positive that if McCain runs in the general election the way he's (wisely) run in the primary - on a platform of victory in Iraq and the Bush tax cuts and porkbusting at home - without coming up with anything else to say to voters, he'll get beaten handily.