WEll asking someone if he is a troll is derogatory and can only mean to incite trouble, however you wish to qualify it. It's certainly reasonable to ask if he enjoys the role of provocateur. And if your real intention is to explore his feelings about May, just ask directly without the insult.
Anyway, I thought May was already banned. The truth is that you can't really ban anyone from a free site. You can make them feel unwelcome, but you can't truly ban them.