Anyone can be blackmailed if they lead a double life. A "conservative" republican who is also a closeted gay man can be blackmailed. This is allegedly what is happening to Graham.
Whenever I see a congresscritter behaving irrationally, that is going against the principles upon which he was elected, I wonder about the blackmail angle. I have concluded the congress system is hopelessly corrupt. It just happens all the time. That is why the only thing that will save us is a 12 year term limit. The power of the incumbency is so very strong.