Originally Posted by: Polar Bear 
So. If it goes through, how will it affect us? (my pay is drawn from the Treasury if that makes any difference to effects)
IMO, this isn't going to work out, so dont hold your breath expecting to see any change at all. But, I will play the game. Here are some scenarios:
1. EO goes into effect and employers play along. Those two line items on your LES for OASDI and Medicare go to 0.00. In my case, that is an immediate increase in take home of a bit over $300/PP.
2. EO goes into effect and employers do not play along. NO effect on take home pay.
2a. Why would employers not play along? Because there is a very real possibility that all that money will have to be remitted after this deferral expires. Employers are responsible for remitting 100 % of the SS and Medicare tax due (50% employer, 50% employee)
3. EO goes into effect, employers play along, and now come the end of the deferral period, its time to pay up. Two scenarios here:
3a. Employers bite the bullet and pay both halves of the SS and Medicare. How many employers do you think are going to do that?
3b. Your (the employee) first couple of paychecks of 2021 are wiped out because all that back SS/Medicare that you haven't been paying for the last 5 months is now due. We have 10 PP left in 2020. In my case, that is over $3k due.
4. This is what POTUS is gambling on: EO in effect, employers play along an stop withholding, deferral period ends. Congress and/or new Administration doesn't have the cajones to come out and say "We need that money now" and collect. Trump is banking on either he gets reelected and he can convince Congress to change the tax law (which would be needed to waive repayment), or if Biden actually tries to collect, he and the GOP can point and say "see, raising taxes already".
Again, I don't see the EO going into effect, but if it does, I would expect Scenario #2 is most likely to play out.