Here at Grant Park in Chicago, the stage for what Barack Obama hopes will be a victory speech on Tuesday night is being set up. On either side of the lectern is a large bullet proof glass screen protecting him from any shots fired by would-be assassins who might be positioned in skyscrapers overlooking the venue.



The bullet proof glass screens that will protect Barack Obama

One of the workers helping build the steel-reinforced stage said the two screens (which measure about 10 feet high and 15 feet long and are about two and a half inches thick) had been lowered into place by cranes at about 5pm today.

He described how Secret Service agents had taken up different positions on the stage where they had been lit up up ont heir chests with red dots apparently "fired" by other agents using laser guns and posing as snipers aiming from the windows of different skyscrapers. The existence of the screens was first reported by ABC radio news.

The screens would protect Mr Obama from most of the high-rise buildings surrounding the park with the line of sight from many other buildings being be blocked by the press stand and broadcast tents . This is the first time I have seen bullet proof screens being used to protect Mr Obama. Law enforcement officials with binoculars often scan tall buildings close to campaign rallies.

Mr Obama first received Secret Service protection in May 2007, a much earlier juncture than previous presidential candidates, after his Senate colleague Dick Durbin raised concerns about his safety. Last week, federal agents in Tennessee broke up what they described as a plot by two white supremacists to assassinate Mr Obama as party of a "killing spree" targeting black people.