Why Wasn't Congress Evacuated Much Earlier?

On the morning of 9-11, a second hijacked jet struck the World Trade Center, at 9:03am. Surely, something was amiss, whether or not individuals or organizations were privy to suspicions of such possible events beforehand. Yet, with the nation in chaos, people staring transfixed at their television screens, and others dying or about to die in the World Trade Center, our Congress was not evacuated.

No, not until around 10:00am, several minutes after the White House was evacuated, 15 minutes after the Pentagon was struck at 9:43am, and almost an hour after the second strike on the World Trade Center, was Congress finally evacuated. I don't know all the facts here, but how could this be possible? We could have lost almost our entire legislative branch.

This should be part of the investigation. How could we be so incompetent with information that, barring the actual prevention of the attacks, once they were clearly underway it took an hour to begin evacuating the halls of American democracy? This is incompetence of the highest order, and someone should be fired.

When the Pentagon was struck, it just as easily could have been Congress, or the White House (which also wasn't evacuated until after the Pentagon was struck). Where was the Secret Service, and how come they weren't privy to the information about imminent terrorist strikes?