They've also been inseparable through happier moments, serving as maids of honor in each other's weddings and working to promote their father's legacy.
But a legal fight over a $19 million gift to the Richard Nixon Library and Birthplace Foundation, the only presidential library that does not receive federal funding, has set the daughters against each other and brought into question the stewardship of the library.
Published reports have painted it as a feud, saying Julie Nixon Eisenhower and Tricia Nixon Cox had cut off communication. But in interviews with The Associated Press, the two women denied such claims and characterized the dispute as a disagreement they were working to solve.
"First of all, we were never not speaking. It's gotten so blown out of proportion. It was a very straightforward difference of opinion," Eisenhower said. "I think because we were so private and refused to talk about it, these stories just got out of control."
Cox agreed, and said the two even continued exchanging birthday cards and letters.
"I've always loved my sister and I always will. We've worked together in the past for the things that we believe, and we are going to continue to do that," she said.
The disagreement stems from a trust left by longtime Nixon friend Charles "Bebe" Rebozo, who died in 1998. It specified the money go to the library foundation but that expenditures be overseen by a three-person board consisting of the two sisters and family friend Robert Abplanalp. A call to Abplanalp was not immediately returned.
Eisenhower, 53, and the foundation want the money put into an endowment under the control of its 24-member board of directors. Cox, 56, also wants the money put into an endowment, but under the control of the three-person board as spelled out by the trust.
After negotiations stalled, the foundation - with Eisenhower's support - filed a lawsuit in February against the Rebozo trust in Florida, demanding the money be turned over immediately.
It also filed suit in Orange County, Calif., asking the court to either hand over the money to the foundation or force Cox, who lives in New York, to sign an agreement putting the money under the foundation board's control.
"We're simply now asking the court to send the money out to California, and we're asking the California court to break the logjam here," said foundation attorney Robert Landon.
Rebozo's attorneys, however, said their client's intent was clear.
"What he intended was to have those three individuals ... control the use of the funds," said attorney Oscar Canabas.
In a letter sent Friday to the foundation's board and obtained by the AP, Cox's attorney, Thomas Malcolm, accused the library's executive director, John H. Taylor, of initiating the current discord.
"By launching a frivolous lawsuit and initiating a media frenzy about a feud between the president's daughters, Mr. Taylor has abrogated his duties to the legacy of the 37th president and the Nixon family," the letter said.
Library spokeswoman Arriana Barrios-Lochrie said Taylor had no comment because he had not seen the letter.
In an earlier interview, Taylor said he was hopeful the sisters' discussions would take both Rebozo's wishes and the foundation's interests into account.
In 1996, the sisters tried to remove Taylor, alleging he cut off their access to staff.
Months later, Eisenhower changed her position and supported Taylor's effort to restructure the board from an informal group of Nixon friends to a larger, independent board of directors. The current board includes former Secretaries of State Henry Kissinger and George Shultz.
Although home to Nixon's pre- and post-presidential work, the library does not house his presidential papers, which were seized after his resignation. As a result, the library does not receive federal funding.
The library supplements its income from admissions, donations and special events, such as weddings. Like many presidential libraries, it rents space for corporate dinners. The annual operating budget is about $3.4 million, with the Nixon Center receiving about $1.5 million.
Eisenhower, who lives in the Philadelphia suburbs, said the Rebozo money would give the library a stable endowment and make it less reliant on raising money from an aging pool of donors.
"I can't imagine that we all can't work it out," she said.
by Chelsea J. Carter