Why Do Conservative Pundits Insist on Telling Democratic Candidates How to Run for Office

There is a notion called truth in advertising.  It should be applied to political punditry.  Any time the pundit writes a column about the Presidential election the column should be preceded by first, the pundits own voting preferences and then second, a disclaimer that the pundits preferences may very well influence the analysis that went into writing the column.
I am reacting, in particular, to today's column by Ross Douthat, The Tempting of Bernie Sanders. It makes two fundamental points, both of which I view as suspect.  The first asserts that Hillary Clinton is ethically challenged.  This appears to be conventional wisdom among traditional Republicans, for example consider this piece, also from today's Op-Ed section.   I asked myself, how much of this is actually true and how much of it is Conservatives repeating it over and over again till it seems true.  My prior is that there have been vile lies spread about President Obama since he took office, so this is the nature of the beast.  It goes with the territory of being the Democratic front runner.