Slavery and the 3/5 Compromise have been banned and repealed by Amendments to the Constitution. Since the 17th Amendment, Senators are at least directly elected by the people of the states rather than the State Legislatures (thank Heavens!) The Electoral College serves no purpose if not needed to protect Slavery [thank Heavens again!]. There was some talk by the Founders that it would serve as a check to the election of a demagogue. 2016 establishes the failure of that idea with the irrationality of the faithless electors of 2016 who demonstrated no coherent plan to stop a demagogue.
Trump lost the popular vote by 2.8 million votes. That is significant. He is to be sworn in as president because of a modest win in the Electoral College after a huge loss in the popular vote. He is not our first president to do so. But the popular vote loss is embarrassing to him as no strong third or fourth party made him a plurality winner as happened in 1992 with Bill Clinton or in 1860 with Lincoln among numerous candidates receiving electoral votes. Trump lost the popular vote to Hillary Clinton. I'm no big fan of Hillary, but her indiscretions pale in comparison to Trump.
And let's not forget why a President Trump would be such a problem: