Along with Sully, people across the US are now mourning the 41st US President - Bush served one term from 1989 until 1993 and oversaw the country through the fall of the Soviet Union and the Gulf War.
Before sunrise, people were waiting to pay their respects as an honour guard stood watch beside Mr Bush's casket in the cavernous Rotunda, which will be open until his state funeral on Wednesday (local time).
Sully came to live with Bush in June, following his wife's death in April.
Vice President Mike Pence said "President Bush was a great leader who made a great difference in the life of this nation".
Former Republican senator and presidential candidate Bob Dole was helped out of his wheelchair on Tuesday to salute the casket of the late former President George H.W. Bush.
At 10 a.m. Wednesday, his casket will be taken to the National Cathedral for a funeral. "He had an enormous capacity to give of himself".
President Trump has declared December 5 a national day of mourning.
He also presided over the end of the Cold War between the United States and the former Soviet Union.
U.S. Postal Service to shut down on Wednesday for National Day of Mourning
This group consisted of Donald and Melania Trump, along with past presidents and their spouses. There will be limited package deliver to avoid backlogs during the holiday gifting season.
Robert F. Kennedy was never president, but he was running for the White House when he was assassinated in Los Angeles in 1968. "But he was also just a good man, who was devoted to his wife, his family and his friends".
Bush took a moment to slip another candy to ex-FLOTUS Michelle Obama during the funeral of his father and 41st POTUS George H.W. Bush.
Dole, 95 years old, shares many things in common with President George H.W. Bush, who died on Friday at age 94.
Bush's service dog Sully visited the casket in the Capitol earlier Tuesday.
The four entrances to the Rotunda were draped in black as Bush's body lay in state, an honor bestowed to only 31 others in the history of the United States (Lincoln being the first president).
The train will bring the former president to his final resting place at the George H.W. Bush Presidential Library in College Station, Texas.
Technical glitch sees Elon Musk's SpaceX Falcon rocket crash land in sea
The Space Coast launch Wednesday will be SpaceX's 16th under the company's commercial resupply contract for NASA . Musk blamed the failure on a hydraulic pump that pushes out one of the booster's four titanium "grid fins".