Ron Klain was a member of Bill Clinton’s 1992 campaign policy and debate preparation staff. (Full biography.)

While Hillary Clinton and Barack Obama have spent the week moving their battle from Pennsylvania to Indiana and North Carolina, John McCain has been fighting a different foe: the dark overhang that the Bush presidency casts on his campaign.

The question of how a presidential nominee deals with a sitting president of his own party is one of the trickiest dilemmas in a campaign — a challenge that is underappreciated by most observers. It is no accident that in the elections since World War II when a candidate has tried to succeed the sitting president of his own party (1952, 1960, 1968, 1988 and 2000), that candidate has failed to capture the White House four out of five times. Elements of Richard Nixon’s inability to escape Dwight Eisenhower’s leadership within his party, Hubert Humphrey’s link to Lyndon Johnson’s unpopular war and Al Gore’s struggle with how to use Bill Clinton on the stump all are present in the complex dance that John McCain is undertaking vis-à-vis George Bush in 2008.

As a result, Senator McCain is spending the week visiting what he calls the “forgotten places” of America. Much as George H.W. Bush’s 1988 declaration that he wanted to have a “kinder, gentler” presidency caused Nancy Reagan to ask, “kinder than who?”, John McCain’s “forgotten places” tour poses the question: forgotten by whom? The places on Senator McCain’s itinerary — Selma, Youngstown and the Ninth Ward of New Orleans — certainly haven’t been forgotten by Democrats: the legacy of the civil rights movement, the economic angst of the industrial heartland and the consequences of the federal failure when Katrina struck have been extensively discussed by Senators Clinton and Obama this year. No, Mr. McCain’s message is inescapable: the places he is visiting are ones that George Bush has forgotten. His tour this week is an attempt to establish some distance between himself and an unpopular president.

But try as Senator McCain might, this effort is doomed to fail for three reasons. First, as others have noted, while Senator McCain has a record of being an independent Republican on issues like climate change and campaign finance reform, the issues he is inadvertently highlighting this week are ones where his record shows no such maverick strains.

In visiting Selma, Mr. McCain brings attention to his opposition to a Martin Luther King holiday and his decisive vote to sustain George H.W. Bush’s veto of the 1990 Civil Rights Restoration Act. At Youngstown, Mr. McCain’s lack of a credible economic plan and his support for extending the Bush tax plan are sure to come up. And in the Ninth Ward, his embrace of a minister who called Hurricane Katrina “the judgment of God against the city of New Orleans” seems unavoidable.

In the end, the 2008 election is likely to be defined by two overarching issues: Iraq and the economy. Senator McCain’s now famous “100 years” remark regarding President Bush’s signature foreign policy initiative makes McCain the Iraq war’s most enthusiastic and visible supporter. And on the economy, the senator not only supports extending the Bush tax plan, he wants to expand it with similar measures that would push the country even more into debt and benefit those who need help the least.

Second, there is a political “box” created by the leanings of John McCain’s own party loyalists. Though President Bush is profoundly unpopular — a 28 percent approval rating in the latest CBS/NY Times Poll — given the arithmetic of the electoral politics a majority (or nearly so) of those who will vote for Senator McCain in November remain Bush backers. Put another way, even if the country is 3-to-1 “anti-Bush,” the 40 percent of the country that is the McCain base is dominated by the minority of voters who approve of the Bush presidency. This dynamic will force a careful calibration on Senator McCain’s part, typified by the fact that his first campaign event, after securing the G.O.P. nomination, was a photo op with the person he least needed to be pictured with to win over the country at large: President George Bush.

Which leads to the final element of the equation: President Bush himself. Most of the analysis of the McCain-Bush question to date envision only a two-dimensional contest, where McCain seeks distance from Bush, and the Democrats pursue him in a pin-the-Bush-record-on-McCain game. But as the days of the Bush presidency dwindle, the president begins to think more about his legacy, and Senator McCain finds himself mired in a close contest, don’t be surprised if George Bush starts itching for more of a role in the McCain campaign, whether the campaign wants the president’s involvement or not. Indeed in late October 2000, when reports emerged of President Clinton’s hunger for the campaign trail (notwithstanding some trepidation in the Gore campaign), candidate George Bush mocked the sitting president’s eagerness to play a role in the contest, saying “the shadow returns.”

Today, eight years later, it is George Bush (far less popular than Bill Clinton was in 2000) who is “the shadow” — the president whose presence cannot be ignored by his own party’s nominee. And no matter how far John McCain travels on his “forgotten places” tour, it’s wise to remember that, as Joe Louis once famously said: “He can run, but he can’t hide.”