I never said that it was illegal to vote for an illegal president. I posted the federal regulation (Administrative Law) which states that two members of Congress (one must be a Senator and one must be a representative) can challenge the Electors of any president-elect and then both Houses of Congress must convene separately and consider the challenge. Members of Congress alleging an ineligible president-elect would have led to a fascinating debate in Congress.
It is the Electors and Congress via votes in a dual session who choose the president, not the popular vote of citizens
Additionally, if an opposition political party controls either House of Congress (or both Houses), members of that party can simply refuse to send any bills to the desk of an ineligible president; thus effectively shutting down the federal government until the usurper resident vacates the People’s House.