AG Barr said yesterday at the House hearing fiasco that he was not aware of any law that would allow the election to be delayed by the President - mentioned the day was fixed by federal statute.
This is all a SETUP to get unanimous support to keep the elections in place. It's the only reason Trump would tweet something that he knows would be so poorly received. Then, when the SHTF, Trump will push forward with the election despite the sky falling on the Dems.