1. A common fear of the executive branch is that the current president and his administration will limit the power of the legislative and judicial branches, leading to a channel of power.
2. Based on the existence of checks and balances, I don't feel particularly fearful of this because of the system's gearing towards making sure no branch can cut off another. However, it is possible for this system to fail through bias. For example, if the president is Republican and the Senate and House majority is also Republican with a majority of Supreme Court judges also being Republican, then corruption is possible through bribery and deals.
3. Constitutional Articles 1-3 explain the limits and powers of all three federal branches. For example, if the president vetos something, it is possible for it to be overruled and passed anyway. I think that in a way this is effective, however, it could be used for worse.