"The Obama years have taught us the sometimes frightening lesson that our Constitution and legal structure alone don't secure the Republic. We also depend on norms - or an implied understanding of what behavior is acceptable."
This is true enough, but Chait then proceeds to exactly the wrong conclusion. We have only become aware of our dependence on "norms" during the Obama years to the extent that they have utterly failed to constrain political power. Republicans have departed from precedent by enforcing the supermajority rule, politicizing the debt ceiling, obstructing routine appointments, and filing suit against the President through the House. From these infamous and unambiguous violations of institutional convention, Chait concludes that Obama needs to maintain another convention, if only to constrain future Republicans?
This is not to say that these conventions are irrelevant - simply that they aren't decisive. It turns out that a Republican president could decide to stop collecting the estate tax whether or not Obama pursues his immigration plans, and that he could decide not to even if Obama does pursue his immigration plan. Historic precedents may play a role here, but if the Obama years have taught us anything, they've taught us that things like partisanship and immediate incentives and a whole host of other dynamics may be even more relevant.