Watergate was a demonstrable crime. White House personnel were caught, staging a break-in to steal political information from another party's headquarters.  The resulting investigation tainted the government, involved the  President in deceitful and possibly criminal behaviour and led to his resignation.  Later investigation and revelation indicated that the President was indeed a 'a crook', or someone with the moral character of a crook. 

So far Trump seems to be what he presents to be - at least publically - we have no way of knowing what his 'official', in-the-office with the door closed persona is. What we do know is that, unlike Nixon, Trump has been under attack, on a personal level, since well before he was elected. That attack has been intensified and now consists of a 'House investigation' into UNPROVEN allegations that A) Russia somehow caused him to be elected and B) that his 'team' (and he) have been, and may still be, "colluding" with Russia to do America harm.