No, Hillary Clinton wasn’t speculating about an Obama assassination.
She was merely using the date of the assassination (June) to point out that not every nominating contest ends in May. Of course, 1968 is the classic case of the Democrats fighting all the way to the convention and not being able to reunify in November, so I don’t think the example supports the argument. But it’s absurd to read anything nefarious into her remarks. And I wish the Obama campaign had resisted the temptation to get huffy.
Still, I would propose a moratorium on the use of that word.