Turns out it's optional. Though you won't find that explicitly stated in either the Order or the recent IRS Guidance "clarifying" it. THAT takes a phone call to the IRS Hotline. But the Agency remains a little foggy on the basis for this conclusion. They're promising yet another FAQ on that part of it.
So ... why? ... amid great fanfare, pomp and circumstance ... did the President dramatically roll out his Executive Order? And declare it a gift to (whom else?) the American worker? And further promise that, if reelected, he would do everything he could to forgive the tax entirely? And ... like a mythical champion of the people ... dare their bosses and congress to stand in the way?
Aside from the legal questions surrounding whether the Executive office even has the authority to do this, there's really no question that the action is a deferral -- not…