I have no doubt that Trump is a smart businessman. You don't accumulate his kind of wealth without making smart business decisions. He is also a brilliant, if shameless, self-promoter, and a master of using the media to his advantage.
But his experience, rather obviously, does not translate into being a serious presidential candidate. His constant stream of banal, sophomoric comments, not to mention his nonsensical platform positions, will catch up with him well before November 2016. For right now, he is able to effectively hide among the large field of Republican candidates. During the first debate, this allowed him to stay on message, offering only sound bites. But as the field narrows, he will have to show that he has full command of some very complex topics. As of right now, he is clearly ignorent on issues of foreign relations, and will continue to stumble badly if directly challenged by moderators or other candidates.
The 24% support that Trump has is among politically-engaged Republicans. These are older, whiter voters who are very angry after 8 years of being a relatively ineffective opposition party. They represent much less than 10% of likely voters. But even if somehow Trump does become the Republican nominee, every study I've seen shows there is no path to him winning a general election with less than 40% of the Hispanic vote. Given his immigration policies, that support is under 10% and dropping. Also, a Trump nomination would strongly energize the so-called "Obama coalition" (young people, single women, African Americans and Hispanics) to turn out in large numbers (and regardless of who the Democratic nominee is).
There is also the distinct possibility that if Trump badly loses a debate, and feels embarrased, he will choose to blame the media and the RNC, and launch a third-party bid. Needless to say, this would be an excellent turn of events for Democrats.