They stood in front of the casket with their eyes closed for a few moments, before Trump saluted the casket.
Attending the funeral will be President Donald Trump and first lady Melania Trump, along with other former leaders and outstanding figures in U.S. public life, including members of the Cabinet and the Supreme Court. And the Trumps visited members of the Bush family at the Blair House presidential guesthouse, where they are staying.
Jeb Bush, the late president's son, had also tweeted the image, saying, "Sully has the watch". "And he did it with modesty and kindness that would have been surprising in someone one-tenth as tough and accomplished as he was", he said.
After services in Washington, Bush will be returned to Houston to lie in repose at St. Martin's Episcopal Church before burial Thursday at his family plot on the library grounds.
John Miller, the president and CEO of America's VetDogs, said the Bush family contacted Walter Reed National Military Medical Center after the late president's wife of 73 years, Barbara, died in April.
Bush's passing has led to an outpouring of remembrances for the humble and gentlemanly statesman, whose life and service was seen to stand in direct contrast to the vitriol and partisanship that has enveloped elected politics in recent years.
"Here lies a great man", said House speaker Paul Ryan.
Side by side, Democratic and Republican leaders laid floral red, white and blue wreaths around his casket. He arrived in the Capitol rotunda in a wheelchair pushed by an aide.More news: Arsenal set for Kiev clash against Vorskla Poltava
After the official ceremony, the public will be allowed to pay its respects.
Governor LePage stated, "I encourage our schools to use the National Day of Mourning as an important opportunity to learn about the life and legacy of President Bush, including such potential topics as the American Presidency, World War II and the Cold War".
Trump will attend the ceremony on Wednesday morning in Washington's National Cathedral along with First Lady Melania.
In an invocation opening Monday evening's ceremony, the U.S. House chaplain, the Rev. Patrick J Conroy, praised Bush's commitment to public service, from Navy pilot to congressman, United Nations ambassador, envoy to China and then Central Intelligence Agency director before being elected vice president and then president.
Millie was famously referred to during the 1992 presidential campaign, when Bush said, of Bill Clinton and Al Gore, "My dog Millie knows more about foreign affairs than these two bozos".
The New York Stock Exchange will also be closed on Wednesday. Offices in Wichita and Sedgwick County will remain open. "He always was caring and treated people equally".
Christy Smith paused over the weekend to pay her respects to Bush at a bronze statue of him at a Houston park.