Ask, are they there? As Churchill was actually in government in both wars and Trotsky was actually a part of the Russian Revolution, of course you could use them as primary sources for those events. On the other hand, when Churchill wrote about his ancestors the Duke and Duchess of Marlboro he definitely was a secondary source.

And though there's constant discussion of historians' biases, primary sources can also be biased and unreliable, often much more than secondary sources. There have been quite a number of world leaders and politicians who have published self-serving memoirs!