Reid stated, "I don't believe in the executive power trumping everything... I believe in our Constitution, three separate but equal branches of government."
"If Obama steps over the bounds, I will tell him. ... I do not work for Barack Obama. I work with him," he said.
Of course, in the same interview Reid says Democrats must be "very, very careful" to avoid overreaching - which implies that Reid's comments about not "stepping over the bounds" is about Obama going too far to the left (signals suggest he has nothing to worry about on that score). So, when you put those two statements together, it may be that Reid is saying that he wants to assert congresional power in stopping Obama from moving left.
All of that said, I agree with the spirit of Reid's comments on executive power and Congress's constitutional responsibilities. We need an active Congress - not a politburo. A vibrant legislative branch is what democracy is all about.