Well, again, it’s pretty hard to quantify how many people are not voting on principle, but again, if we use third-party voters as a guide, that’s probably not true. For Hillary, analysis shows that even if every single Jill Stien voter had gone to Clinton, she still would have needed to win over 50% of Gary Johnson’s voters (who were obviously unlikely to consider themselves leftists) to win..

Bush and Gore is different, since Bush won by 537 votes in Florida, so sure, if the Nader voters had gone to Gore, he would have won. You could probably also assume that there were 537 disgruntled leftists who decided to stay home as well, but with a margin that small, almost anything could have changed the outcome. If all the voters who stayed home with a cold went out and voted Gore might have won.

You’re working from a premise that there’s a large contingent of leftists who are withholding their vote on principle, and if they just voted, the Democrats would always win. But there’s no data to assume that’s true, and it’s just as likely that there are as many conservatives doing the exact same thing. So what’s point here? If only all the leftists who didn’t vote on principle came out, but all the conservatives who didn’t vote on principle still stayed home, things would be different? You could blame pretty much any group for your candidates’ loss with logic like that.