How so? She isn't even a candidate yet, and may or may not decide to run. If she does, it will be as a Republican in the primaries, not a 3rd party spoiler. If she wins the nomination it will be because more Republicans wanted her than anyone else. That's hardly a spoiler. If it happens then it's up to the moderates to get behind the nominee the way they always tell conservatives to support RINO nominees.
BTW, I'm not a Trump supporter, but he is talking about running for the Republican nomintaion, not running as a 3rd party, which is a huge difference from Perot.
All battles are won or lost before they’re ever fought. The primary election is where a general election battle is either won or lost. The Republican party has developed a bad habit of not learning this lesson. More to the point, I have already heard numerous conservatives asserting that they will not vote for Donald if he is picked over Sarah Palin. That means they would be the ones spoiling the election, not Donald Trump.