One is past tense and the other is present tense. So, "I think Donald Trump is a bad for America!" - you might say, "Yes, I have always said that" meaning you have been saying it for some time, perhaps even before he was elected, but you haven't necessarily said it recently. Now if I say, "I think Donald Trump is a fantastic president!" and you say, "Yes, I am always saying that!" you probably mean that you keep seeing negative things written about him but every day - including today - you disagree with them. Does that help?