What did Donald Trump do today?

He got so far out on a limb trying to bribe voters with tax cuts that even Steven Mnuchin couldn't bail him out.

Yesterday, en route to still yet another campaign rally, Trump told reporters that he was "looking at putting in a very major tax cut for middle-income people." Bizarrely, he followed up that vague hint with an impossible deadline: "And if we do that it’ll be sometime just prior, I would say, to November."

As Trump (hopefully) knows, changing tax laws would involve passing a bill through Congress. Congress is not in session and will not be again until November 13. Since tax policy affects every American, and is the way that the government funds itself, even minor technical changes normally take months of planning.

Pressed for comment today, Treasury Secretary Steven Mnuchin--who presumably would have been in the loop on any actual plan--had no explanation for what Trump may have meant.

It's not unheard of for politicians to try to tempt voters with the prospect of lower taxes, but Trump may want to be careful about doubling down on this particular bribe. While the 2017 tax cut package was his one and only significant legislative achievement, it has not been popular. While it has resulted in enormous windfalls for corporations and real estate tycoons, most Americans--and hence most voters--have seen no real change in their tax bills, and the ballooning budget deficit it is causing hasn't helped either.

Why should I care about this?

• Tax policy can't (and shouldn't) be made up on the spot.

• Past a certain point, campaign promises can be so obviously fake that it becomes insulting.

• It's bad if we genuinely can't tell whether a president knows how a bill becomes a law.