Stuart Stevens has just published an article recommending something like the approach I've been recommending against Trump. The way I put it in January, on Facebook, was that Trump should have a nuclear bomb dropped on his head every day. Bring up how he boasts about committing adultery with so many women, his business failures, his poor electability, etc. Hit him hard, relentlessly, from every direction. Since the media are so unwilling to give him a full vetting, which they'll surely give him if he becomes the nominee, let's give him that full vetting now rather than later. It doesn't look like Cruz, Rubio, Bush, or anybody else is going to take this sort of approach anytime soon, but they ought to.
Here's an article by Kevin Williamson about some of Trump's business failures and dishonesty. It provides some examples of what could be used against Trump, but seldom is.