Could Watergate happen again?

Most certainly – and I mean both the initial scandal and the resulting over-reaction of the reformers.
All of the so-called Watergate reforms have been ineffective – and the abuse of institutions remains a constant threat. Put simply, you cannot legislate morality.
The Founding Fathers had it right: they greatly feared concentrations of power and hit upon the solution of three co-equal branches operating in a system of checks and balances.
When you get bright and self-assured officials who are so committed to their particular point of view that they decide that their ends justifies their means, then you get the conditions that led to Watergate: intellectual arrogance and institutional abuse.
All that’s then needed for a national scandal is when the political pendulum swings back the other way – and you get a Congress willing to take on the President and, perhaps, a special prosecutor.
Special Prosecutors are an invitation to abuse: when a group of specially-recruited, highly partisan prosecutors is assembled to target a specific group of individuals, our Fifth Amendment’s guarantees of due process seem to evaporate in the rush to secure convictions.
The greater the perceived abuse from the one side, the greater the over-reaction from the other.