His son and 43rd U.S. president George W Bush posted an Instagram photo of Sully lying in front of his old master's casket on Sunday.
Mr Bush's remains will travel back to Texas on Wednesday, where he will lie in repose at St Martin's Episcopal Church in Houston with a funeral service the next day preceding his interment at the George Bush Presidential Library in College Station.
To commemorate the first former president to die since Gerald Ford in 2006, officials have announced a detailed, four-day schedule of celebratory services and tribute, organised with military precision by the Pentagon task force charged with protecting the U.S. capital.
Meanwhile, the City of Houston is honoring George H.W. Bush with a City Hall tribute and is urging people who attend to dress in colorful socks. The number is a reference to Bush's place in the roster of America's presidents.
He added: "A lovely day In Texas - 'ceiling and visibility unlimited, ' Mr. President".
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From there, a departure ceremony will be held at 10 a.m. on Wednesday before Bush's casket is transferred to the Washington National Cathedral at 11 a.m., where a funeral service will be held for family and friends.
Trump, who has not always uttered kind words about the Bush family, offered nothing but praise in the hours after the former president's death was announced. It is anticipated that foreign leaders will also be paying condolence calls to the family on Tuesday. Former Canadian prime minister Brian Mulroney told Politico he will deliver one of several eulogies at the service, at Bush's request. There, he cancelled a press conference "out of respect for President Bush" and ignored a reporter who asked if he regretted any of his comments about Bush or his family.
"But he was alert", Baker said during a blitz of appearances on five Sunday talk shows.
Sully, the service dog of President George H.W. Bush, keeping watch over his best friend.
That was a time that saw the end of the Cold War as well as the United States' routing of Iraqi President Saddam Hussein's army in the 1991 Gulf War.
Colin Powell, who was chairman of the Joint Chiefs of Staff during that war, said he was confident in Bush's leadership because, as a World War II veteran, "He knew what combat was all about". "He knew that combat meant the death of people, people on your side and people on the other side. He wanted to avoid a war".
President Bush had been receiving treatment for a form of Parkinson's disease and had been admitted to hospital with a blood infection in April. "And he led a full life, and a very exemplary life too, I will say".