Not a whole lot. Maybe you could see it from the Eisenhower Executive Office Building, but that’s basically an extension of the White House, so I assume it’s guarded just as heavily.
I’m not challenging kunilou, but the protagonist in The Day of the Jackal (1971) made bardos’ claim. The novel describes the work of a professional assassin, hired to kill President DeGaulle.
When we visited London about 12 years ago, I looked up where the Queen was going to be on her website and we staked out the place. She got out of her limo for an event at the National Portrait Gallery maybe 30 feet from us.
The only people in front of us were some old ladies who seemed to be there to wave little flags - until just before the queen appeared and they pulled out enormous cameras and started snapping away… 
the last time I shook hands with a Canadian Prime Minister, in the 80’s, there was maybe 2 or 3 Mounties with him. The campaign staff probably outnumbered security.
When the pope drove down the street in Toronto (before the attempt on his life in ROme, IIRC) there was maybe a few police cars before and after him; I was standing on the curb, he wasn’t more than 25 feet away. In Rome, a few years before he died, he drove by the crowd down teh center of St. Peter’s “square” in an open-top limo and I stood on a chair maybe 10 feet away to get some pictures. There looked like about 4 or 5 “secret service” types walking alongside the car.
The level of security around any foreign leaders in miniscule compared to the US President.