How is Trump different from other candidates? He can't utter two coherent sentences in a row. He can't articulate any of his policies. His policies, to the extent they are presented, are half-baked gobbledygook. He's picking up endorsements from Republicans whose alternative opportunities are as guests on Celebrity Apprentice or Dancing with the Stars.
Trump doesn't speak the truth, he speaks gibberish. Trump appears to have no self-restraint which also appears to be a characteristic of reality TV stars. It's a little like having Kanye West or Kim Kardashian as the leading candidate and Kardashian has more self-restraint.
Rubio and Cruz has started what could be an effective counter to Trump. Had one of the candidates done that in October or November Trump would be gone by now. They have only scratched the surface of an iceberg that includes the USFL, Trump Shuttle, Trump Mortgage, the Grand Hyatt Hotel, the Plaza Hotel, four casino companies (three created after the bankruptcy of the prior one), Trump University (which he is now defending in his speeches), Trump Baja, the now Chinese-owned New York Military Academy (which was sold at a bankruptcy auction last year), foreign labor at his Florida catering hall, Polish labor building Trump Tower, etc.
The only question is whether there is enough time left and enough money to be put into marketing to make the attacks stick. Trump supporters now have to be dissuaded after they have built up relationships in affinity groups and formed their opinions. They won't listen to counter arguments. It will take a lot of advertising - short, hard-hitting advertisements - and social media repeated over and over again. Billboards would also work as would drive time radio. The key is going to be lots of repetition of the wide variety of Trump failures with the key common conclusion: things Trump touches turn in the garbage and Trump himself is a loser.
Trump's only counter argument is going to be that he may have a current net worth $4 billion. That's going to need to be countered, as Rubio and Cruz have already started, by showing that it is only because he started with his father's fortune, has lucked out with foreign investors buying US properties, and low interest rates. You also have to compare him with other investors and business people, showing how they succeeded when Trump failed. Sheldon Adelson, Steve Wynn, and any number of New York City real estate moguls will provide a counter example.