Single 4-year term is too short - you are out before you learn anyting.
What modern president had a second term better than his first?
You are basing your statement on the theory, that the problem with the second term is that it is second. I would propose an alternative theory, that the the problem is that it is last. If my theory is correct, you would get the worst of both worlds: inexperienced lame duck from day 1.
No, no. I think the reason second term presidents are ineffective is because it is the last term. That is why I support this new amendment: in order to make every president less effective.
However, your argument is that a one term limit is too short, because you're out before you learn anything. But because under the two term limit that you support, the second (experienced) term is actually 'worse' (from the president's standpoint) than the first, I don't understand your view.