Today's a new day

According to the 9/11 Commission Report:

When they learned a second plane had struck the World Trade Center, nearly everyone in the White House told us, they immediately knew it was not an accident. The Secret Service initiated a number of security enhancements around the White House complex. The officials who issued these orders did not know that there were additional hijacked aircraft, or that one such aircraft was en route to Washington. These measures were precautionary steps taken because of the strikes in New York.

Question: Why did the Secret Service allow Bush to remain in the classroom of the Emma E. Booker Elementary School after the second plane struck, when according to then Chief of Staff Andrew Card, "America is under attack?"

The President remained in the classroom for another five to seven minutes, while the children continued reading. He then returned to a holding room shortly before 9:15, where he was briefed by staff and saw television coverage.

This passage does not describe the Secret Service trying to hustle Bush out of the building in those minutes -- not even suggesting it. Why not?

Compare and contrast with how Cheney was treated 20 minutes later:

This news prompted the Secret Service to order the immediate evacuation of the Vice President just before 9:36. Agents propelled him out of his chair and told him he had to get to the bunker. The Vice President entered the underground tunnel leading to the shelter at 9:37.