One addition: I think that the terrorists should be forced to do duty too.Not just the security members.Because what is the point of them staying behind fighting policemen?That's no assassination attempt to me.
The solution is simple: make them follow duty by forcing them to chase the president, disallow chasing policemen to do statswhoring, jail/ban people who only go around dueling policemen/SWAT. I think you should also make terrorists respawn after a president dies, so they would not retain armor advantage after dying, plus possible proximity advantage (if they are closer to the president spawn than they would be from their own spawn after respawning).Another advantage they get is taking armor and eventually maybe grenades while there is no president, so they keep all the benefits, and do not respawn after a president shows up, so they can attack him very swiftly if they are near his spawn.
OR: create a terrorist class that naturally opposes security class, have them equipped with armor, and have THEM attack the president mandatorily.