My father is about to become a islamic extremist, what do I do?

My father, a formerly very devout christian, devoted all his savings and efforts to prove that islam is a false religion. I was shocked to hear that six months ago he stopped attending his church and last month he officially became a muslim. I don't see why he would do that, I know that muslims are peaceful people but he might as well choose to become an extremist terrorist zealot. Right now I'm deployed overseas but I'm willing to spend some more time with him in the coming months. How do I talk him out of it?