DENVER — For four days, speaker after speaker rose up at the Democratic National Convention to assail the Republican Party’s record, rail against President Bush, capitalize on economic anxieties, appeal to the public’s discontent with the war in Iraq, and argue that John McCain represented more of the same. What they did not do, at least not very consistently, is make a positive case for Barack Obama.

Now the Republicans get their turn. They don’t have to try to convince a skeptical public that a man who was in the Illinois state legislature just five years ago is ready to lead the free world. They don’t have to make the job of community organizer sound similar to that of a commander-in-chief. But the Republicans are heading into St. Paul with problems of their own.

The first problem they plan to get out of the way quickly, on the very first night of the convention: the deep and enduring unpopularity of President George W. Bush and Vice President Dick Cheney. In Denver, “Bush-Cheney” was uttered like a curse. The incumbent president has a 30 percent job approval rating in the latest CNN poll.

At first glance, that should be easy enough to solve. Hide Bush and Cheney away at, of course, an undisclosed location. The actual nominee remains popular with independents and is still polling competitively while the GOP dog food is being taken from the shelves. Highlight McCain’s independence from Bush and his compelling personal story to make the Democrats’ cries of “Bush-Cheney” seem puerile.

Easier said than done. Many of the people who prefer Bush to McCain will be sitting in the convention center in St. Paul. Conservatives distrust McCain, who sided against them on tax cuts, immigration, embryonic stem-cell research, global warming, campaign finance reform, regulating private gun shows, and multiculturalism. A post-Reaganite “Sam’s club” running mate may not be enough to reassure skeptics on the right.

Thousands of Obama supporters were willing to wait outside all day in the hot sun to hear their candidate speak at Mile High Stadium. Comparable enthusiasm from McCain supporters is hard to find. McCainiacs need to rely on Obama to be inspiring too — to be liberal enough to inspire conservatives to vote against the Democratic nominee in large numbers.

It may happen. But Republicans don’t want to rely solely on Obama to mobilize their base, so they are already busily papering over the differences between McCain and the rest of the party in an attempt to bring disgruntled conservatives back into the fold. That starts with the platform, which was being hashed out before the Obama coronation was complete.

A preliminary draft of the Republican platform is short on references to McCain — in stark contrast with the Bush-centric platforms of 2000 and 2004 — and tries to split the difference between the nominee and his conservative critics. On immigration, for example, the platform says, “We oppose amnesty. The rule of law suffers if government policies encourage or reward illegal activity.” The guest-worker language from four years ago has been deleted and replaced with a call to finish the security fence along the Mexican border.

Is this a harsh repudiation of McCain’ stance on immigration? Not exactly. There is also language comparable to the presumptive nominee’s rational for flip-flopping in favor of enforcement-first: “The American people’s rejection of en masse legalizations is especially appropriate given the federal government’s past failures to enforce the law.” Plus, it contains a section on “embracing immigrant communities” that advocates assimilation in terms that could be embraced by every Republican from McCain to Tom Tancredo.

The Republican platform committee has also taken the middle ground on global warming, neither endorsing costly cap-and-trade nor condemning McCain for embracing the approach himself. Instead there is conservative rhetoric about “market-based” solutions that avoid “doomsday climate change scenarios,” mixed with vague wonkery without easily identifiable ideological content.

Without conservatives, McCain has no chance. But he needs the independents who dislike Bush but are not convinced Obama is qualified to put him over the top.

McCain’s challenge next week is to be able to defend conservative policies in their own right independently of Bush — even though he has not always agreed with those policies — while raising the threshold question of this election. If the question is simply which candidate will break definitively with Bush, Obama wins. But the Democrats have not sealed the deal on their candidate’s qualifications and their own policies. If he is to become president, John McCain can’t let them.