To be clear, Trump does not have the authority to do this. The constitution explicitly states that "The Times, Places and Manner of holding Elections for Senators and Representatives, shall be prescribed in each State by the Legislature thereof; but the Congress may at any time by Law make or alter such Regulations, except as to the Places of chusing Senators"
That is, federal elections are governed by the states and by congress, not the president.
https://apnews.com/article/voting-elections-trump-executive-order-4e9edb53f47e61e241a43ceef8164022