>Trump has the power to do anything that people (especially Congress) does not push back against.

Elections are run at the state level, so it's not like Trump can direct state agencies to stop counting mail-in ballots. That said, the fact that elections are run at the state level, and the fact that only a handful of swing states matter means it only takes a few pliant election officials to change the outcome of the election. eg. if Georgia's governor caved in 2020.

> Elections are run at the state level, so it's not like Trump can direct state agencies to stop counting mail-in ballots.

Trump asked Texas to redistrict that they were all for it.