Demand a full and accurate prospectus from the Business Leader
Mitt should fully disclose everything. Period.
All the tax returns he gave John McCain, plus the ones since then.
All the documents related to his relationship with Bain and its associated companies and other organizations (whatever their actual name and category might be).
Full accounting of his offshore accounts. And any in his wife's name.
Not merely what the law requires. Not "more than this, less than that". Not just the minimum he can get away with revealing. Everything.
Sure, usually that information is considered private. This isn't usual.
How much he made and how he made it has a direct bearing on his potential presidency, because that's supposed to be his strength: that his monetary success gives him expertise and vision to lead the country as a whole.
If keeping it private is that important to him, then let him stay a private citizen. If he wants to be president, if he wants the broad public to "invest" in him with their votes, then he needs to put forth a compete and accurate prospectus. He can monkey around all he wants, but nobody is obligated to vote for him.
(well, nobody except the guys the Republican Party made sign loyalty oaths)