CHICAGO — In the nearly 60 years since the federal government became the official caretaker of former U.S. presidents’ historical documents, presidential libraries have engaged in a delicate dance to keep the private foundations that build them and the taxpayers who keep them running from stepping on each other’s toes.

While presidential libraries are designed and built almost entirely with private donations, they are then handed over to the National Archives and Records Administration to oversee.

With the site-selection process under way for President Obama’s library and museum, attention has returned to the amount of federal money it takes to operate and maintain these facilities.

Last year, it cost taxpayers nearly $68 million — the equivalent of about 21 cents per U.S. resident.

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That’s a drop in the bucket in the federal government’s $3.5 trillion budget. But the notion that taxpayers are footing the bill to run 13 presidential libraries, with another on the way, doesn’t sit well with everyone — including those who view them as “museums of spin” to shape public opinion.

While the major responsibility of the National Archives is to preserve and make accessible the presidents’ papers, records and other historical materials, the libraries also are considered to be repositories of history for the public.

But it isn’t always clear where the government’s work begins and where that of the foundation — the nonprofit whose mission is to ensure that the president’s vision for his library is carried out — ends.

The relationship varies from library to library. In most cases, the foundation continues to occupy offices in the library even after the building is deeded to the National Archives.

While the federal government covers most staffing, maintenance and operational costs, foundations often pay for programs and exhibits. The government pays for building repairs, but major exhibit renovations generally are handled by foundations.

It is a complex relationship that makes some taxpayers uncomfortable.

The George W. Bush Foundation, which operates the George W. Bush Institute, occupies more than half the 208,000-square-foot Bush Presidential Center on the campus of Southern Methodist University in Dallas.

The foundation also operates the gift shop, cafeteria and auditorium.

In addition to the museum and library archives, the Clinton Presidential Center in Arkansas also houses the Clinton Foundation and the Clinton School of Public Service, an extension of the University of Arkansas.

“The public is sometimes confused by this private-public partnership,” said Benjamin Hufbauer, a presidential library scholar and associate professor at the University of Louisville.

“They are basically museums of spin established by the presidents … but they want the federal government to run them and give them legitimacy.”

But Susan Donius, director of the National Archives’ Office of Presidential Libraries in Washington, said presidential libraries are important to democracy.

“Ultimately, by having presidential libraries located around the country, we give American people firsthand access to democracy,” Donius said in an interview with the Chicago Tribune earlier this year.

“We have a curatorial staff that oversees the exhibits, but the story is the president’s to tell. It emphasizes the points he wants to make about his four or eight years in office.”

The problem, according to Hufbauer and other library experts, is that the libraries and museums rarely fully acknowledge mistakes or problems that occurred in the president’s administration. And if they do, they have a way of making the missteps seem like they weren’t so bad.

At former President George W. Bush’s library dedication last year, former President Clinton joked that the new building is the “latest, grandest example of the eternal struggle of former presidents to rewrite history.”

While the archival function is crucial to the libraries, the National Archives has been so short-staffed that a large backlog of presidential items waits to be archived. According to a 2010 report by the Congressional Research Service, it would take the National Archives 100 years to catch up.

Officials said that backlog has been reduced significantly but that they have not kept pace with the influx of new documents.

The modern concept of presidential libraries began in 1939 when President Franklin Roosevelt donated his personal papers to the federal government and formed a nonprofit group to raise money to build the library on his estate in Hyde Park, N.Y.

When President Truman decided he wanted a library, too, Congress passed the Presidential Libraries Act in 1955, creating the system of privately erected and federally maintained libraries.

As the number of presidential libraries grew, Congress passed an amendment in 1986 requiring the foundations to create a private endowment to offset increasing operating costs.

The George W. Bush Foundation, for example, raised more than $500 million to build the library and cover the endowment.

Under a 2008 law, Obama will be required to have an endowment equal to 60 percent of the cost to build the library; his most recent predecessors needed to reach only a 20 percent threshold.

The endowments come as the National Archives’ presidential-library spending has seen modest declines, from $70 million in 2007 to $68 million in 2013.

With presidential libraries costing upward of a half-billion dollars, foundations could find themselves hard-pressed to raise enough money from private donors — a problem that watchdog groups said could make them susceptible to abuse.

Library foundations are not required to disclose the identities of donors. Since fundraising for the library begins while the president is still in office, there is the potential for it to affect policy decisions, watchdog groups said.