Literally every election is decided by the “undecided”. Democrats vote democrat and republicans vote republican. It rare that anyone changes party. What determines elections is if democrats can get people who wouldn’t otherwise vote to vote. Every time people turn out, democrats win. When people are uninterested they lose. Those ~50k people in suburbs of swing states are not unimportant, they are the only thing that matters.
Yeah, there’s a big difference in protecting Obama or Bill Clinton who are retired statesman living peaceful lives and Trump who has been rallying for the last decade. How much protection is he really entitled to? Especially considering his rhetoric is motivating his would be assassins.