Assume that 60% of registered voters vote in each state ( a generous assumption). Figure out the smallest voting population of states that could provide a candidate with a win in the electoral college. What is this as a percentage of the national total of registered voters? The tables below give the electoral votes and the number of regisrtered voters in each state. (Note: there are 504,000 registered voters in the District of Coumbia, which has 3 electoral votes.)
More realistically, consider the 2020 election results and the six states where Trump has falsely claimed fraud: Arizona, Georgia, Michigan, Nevada, Pennsylvania, Wisconsin. Determine how many votes would need to be taken from Biden's total and in which states so that Trump would win by 10,000 votes in those states and would win in the Electoral College. Do this so that the votes taken from Biden are as few as possible. Calculate the new national popular vote totals. The politico electoral map link gives state-by-state votes.
Electoral College -- table of electors for each state
Registered voters in each state
Spreadsheet with Elcetoral College and Population