proponents of that position should at least recognize that they're changing the "rules of the game" and dispatching with certain "norms" around how presidents are treated at the very beginning of their terms...at least acknowledge the shift.
It's not clear to me why one would need to "acknowledge" any such thing. Why not simply proceed on the understanding that the shift has taken place, and address any objections to that claim as they arise? Tracey himself concedes that "it could well be right to hold Trump to a different standard," so I don't see anything that necessarily needs to be explained or defended here. As far as I can tell, some people believe that the previous rule no longer applies, and no one - not even Tracey - has actually contested this judgment.
That said, setting aside the burdens of explanation, the rationale for a rule change strikes me as fairly obvious. A standard perspective on the past eight years holds that Republicans pursued a historically unprecedented strategy of near-absolute obstruction - popularly known as the McConnell Strategy - in order to guarantee gridlock under a Democratic president. It was this strategy that liberals demanding cooperation with Obama were reacting to; it was this strategy, and not its opponents, that "changed the rules of the game" and "dispatched with certain norms" of American politics.
What I puzzling is not that some critics have called for Democrats to play by the new rules, but that Democrats, to the last Senator, have insisted on playing by the old ones. Every one of them has now cast at least one confirmation vote for one of Trump's nominees. Even Senator Dick Durbin - who in 2010 openly acknowledged that Republicans were simply working to "deny the president a record of accomplishment" - has now voted to confirm Trump's Secretary of Defense, his Secretary of Homeland Security, and his Ambassador to the United Nations.
As far as I can tell, Tracey also seems to think that we should play by the old rules. What this means, of course, is that Republicans will continue to advance objectives amenable to Republicans, while Democrats will find themselves trapped in gridlock for the foreseeable future. If we are to accept this state of affairs for the sake of maintaining some kind of foolish consistency, I can appreciate Emerson's thoughts on that point; but regardless, I don't see anything overtly wrong with playing by the new rules, so if Tracey has objections, he should actually spell them out.