From Letters from an American:
Another of Trump’s memos relies on the law that gives the Treasury Secretary leeway to delay tax filing and collection in case of disasters. Trump directs the Treasury Secretary to defer payroll taxes for workers making less than about $100,000 a year, starting on September 1. Members of both parties disliked this idea, but it has long been one of Trump’s favorite provisions. He insists it will inject money into the economy, although there is argument over that.
The taxes would still be due, just not until next year. But Trump appears to want to end them altogether. Trump’s lawyer Jenna Ellis tweeted “This is actually the biggest news of the day: President Trump said that if he is re-elected, he will look into terminating the payroll tax permanently!”
It is the payroll tax that funds Social Security and partly funds Medicare.