Why is the Secret Service barring very tall protesters from George W. Bush's inaugural?

According to today's Washington Post, the Secret Service will not allow a group of protesters on stilts to gather near the White House because the stilts could be used as weapons.

Who does the Secret Service protect?

The president, vice president, president-elect, and vice president-elect, and their immediate family members. Also former presidents and their spouses and their children, up to age 16. This means that Bill and Hillary Clinton will continue to get Secret Service protection when Clinton leaves office, but Chelsea will finally be free to go on a date without being chaperoned by an armed agent. The Secret Service also protects major presidential candidates (the secretary of the treasury decides who's "major") and visiting foreign leaders. The president can also ask for temporary protection for other people. For example, the Secret Service guarded the pope on his last visit.

What's all this cost?

This year's budget authorization for the Secret Service is $832 million, up from $691 million last year, but protection is only one of the agency's assignments. The Secret Service, a division of the Treasury Department, also investigates financial fraud such as counterfeiting--its original mission when it was founded in 1865. More is spent on protection than fraud investigations, but the Secret Service does not reveal the actual breakdown.

Could Laura Bush decide she doesn't want protection when she becomes first lady, or could Hillary Clinton decline continued protection when she becomes former first lady?

Yes. Only the president, vice president, and the president-elect and vice president-elect have no say over whether they get protection. By law, everyone else can waive theirs, or in the parlance, "sign off." The Secret Service would not comment on whether anyone ever has. (Explainer is betting few people want to give up having good-looking armed guards drive you to the hairdresser.)

[Addendum, Jan. 11: As several alert readers pointed out, in 1985 Richard Nixon dropped his Secret Service protection, saying it was a waste of taxpayer money. The previous year he had dropped Pat's, who apparently made it back and forth from the hairdresser's on her own without incident.]