Twenty years ago this Sunday, a truck bomb exploded next to the Alfred P. Murrah Federal Building in Oklahoma City. One hundred sixty-eight people were killed in the blast, hundreds were injured.

The bombing prompted heightened security at federal buildings — around the nation, and especially here in Washington.

One of the government’s first responses to the bombing was closing a two-block stretch of Pennsylvania Avenue in front of the White House.

It had been a major thoroughfare in Washington, dubbed “America’s Main Street.” It was busy with car and truck traffic from the Capitol, to the White House and west to Washington’s original commercial center, Georgetown.

Oklahoma City Bombing A 'Wake-Up Call' For Government Security : It's All Politics : NPR

We banned vehicles, we didn’t ban good ol’ Catholic white boys.

Amazing how that worked out.