It's amazing the amount of worrying going on about the prospect of Donald Trump winning the presidency. Granted, it would be a disaster if he did win, unless you want a president who is a liar, a cheater, a narcissist, unqualified, stupid, and racist, with fascistic tendencies.
But Donald Trump will never be elected President of the United States.
(1) If Trump won the Republican nomination, the party establishment and the conservative ideologues would be horrified. He is far too unpredictable and unreliable to fit their mold. There would undoubtably be a third-party run with a candidate who would appeal to the conservative base. That would mean a three-way race between a Republican (Trump), a staunch conservative (Paul Ryan? Mitt Romney?), and the Democratic nominee. That would split the Republican/conservative vote, making it easy for the Democratic nominee to win a plurality, if not a majority, of the votes.
(2) If the Republican Party were to block Donald Trump from becoming their nominee, instead nominating a more reliable right-wing candidate, you can bet Donald Trump--with an ego bigger than Texas--would not sit out the presidential race. In this scenario, Trump would certainly run as a third-party independent, and as in #1 above, split the Republican/conservative vote and present the presidency on a platter to the Democratic nominee.
Nothing has been as unpredictable as politics in this election cycle, and strange happenings will probably continue to occur until November 8. Still, It's hard to imagine one of these two scenarios above not occurring, and in neither one does Donald Trump become President. Take a deep breath, America, we will not see a President Trump, but more likely another President Clinton or a President Sanders.