Yet current and former security specialists say that such screening procedures usually can't catch the kind of zealots Obama might attract.
"He brings dynamics into this that we haven't seen before. And they can't be taken lightly," said Joseph J. Funk, a former top Secret Service official who spent eight years protecting Presidents George H.W. Bush and Bill Clinton.
Obama will remain safe even if some event causes a stampede during his inauguration or along the parade route, said Funk, whose U.S. Safety & Security firm headed Obama's campaign security until spring 2007. The incoming president will have secure escape routes and other contingency plans.
The Secret Service took over security for Obama in May 2007, at the earliest stage ever for a presidential candidate.
"Your concern is the person who wants to make a statement, the person who wants to use this as the day to 'make myself famous,' " Funk said. "You can't get to the president to cause harm, but you can hurt a lot of other people and cause an embarrassing situation. You know there's enough media here, and you think, 'Watch this.' "
Few protections exist against such assailants, Funk and others said.
Metal detectors will screen ticket holders to events. All inaugural personnel -- even waiters and doormen -- undergo criminal background checks. But there are always last-minute replacements and changes in plans.
There will be pressure for security to be unobtrusive, and to avoid aggravating long waits, especially where VIPs are concerned.
At that, most would-be assassins of political figures -- such as John W. Hinckley Jr., President Reagan's assailant -- would have passed background checks anyway, because they had never done anything wrong before.
Authorities warn that attackers could also strike soft targets that are virtually impossible to protect, such as hotels, mass transit and large crowds at inauguration-related concerts and other events.
The FBI and Department of Homeland Security warned of such Mumbai-style attacks on the inauguration in a recent confidential Joint Threat Assessment, portions of which were leaked to reporters.
"How do you predict what is in a person's mind?" said FBI spokesman William Carter. "A person who sits in their basement and self-radicalizes or has some type of grievance and decides to take some action -- that is part of the makeup of the lone-wolf individual. They fall below the radar."
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josh.meyer@latimes.com
Times staff writer Julian E. Barnes in Washington contributed to this report.
