1.
If you say that it is ~ that something is true, you believe that it can be supported by evidence and that many people would agree with it. (FORMAL)
It is ~ that this was not as grave a handicap as it might appear...
ADJ: oft it v-link ADJ that
2.
An idea, point, or comment that is ~ is not obviously true or correct and should be questioned. (FORMAL)
It is ~ whether he ever had much control over the real economic power...
= debatable
ADJ: usu v-link ADJ, oft it v-link ADJ whether