Governor Jeb Bush and Doctor Ben Carson need to stay out of the 2016 Presidential race for the good of themselves, the Republican Party and the country as a whole.
Governor Bush is already talking about running a "pragmatic" campaign - pro-established businesses, government-oriented, in the style of Bob Dole, John Huntsman, John McCain and Mitt Romney. It is the only Presidential campaign model with a 100% failure rate, despite Governor Bush's erroneous claims that it hasn't been tried before. Governor Bush has also displayed an unfortunate trend towards imposed, top-down orders and against bottom-up natural solutions, as his support of Common Core shows. Top-down has been demonstrated as a clear failure by the Obama Administration - the country doesn't need someone to try and "do it right", and it is the wrong direction for the party to go in.
And then there's the issue of his family - America doesn't need dynastic politics. We already have the problem of the presidential path being informally limited to a handful of the most prestigious schools in the country. We don't need the Republican Party to become the Bush Party. Also critical, President Bush's negatives are still high, and it will be too easy for Democrats to run against Bush by running... against Bush. Jeb Bush is not the only qualified option the Republicans have to take the White House, and he may not even be the best. But there are a number of primary voters who would vote for Jeb Bush because he had a familiar name, or as a "screw-you" to the Democrats, thinking either that the election is already decided or that the GOP needs to run another "inoffensive" candidate like Bob Dole or Mitt Romney.
Doctor Carson brings a different set of problems to the table. Doctor Carson has an impressive resume as a physician and public speaker. Unfortunately, he has no executive or serious leadership experience. While there are many positions that require executive or leadership skills, a neurosurgeon is not one of them. We have seen, with the current Administration, the results a failure of leadership has on the government. The Veterans Administration is the clearest example of this - there appears to be no political corruption, but the agency deliberately withheld care and buried negative information with apparently no serious oversight. The wide-ranging failure of the VA has no direct political implications, but is simply a failure of leadership on the part of President Obama.
He has also clearly not developed an ideological basis on which to make policy judgments. Effective leadership in politics demands some standard by which to make policy choices and that requires some philosophy of governance. Doctor Carson is right on some issues, and wrong on others, like guns. This is apparently because he is making policy choices based on his own personal experience, and not from a sound philosophical grounding that can justify a position to the nation as a whole.
But Governor Bush and Doctor Carson both have a great deal of name recognition and will draw a lot of attention away from other candidates in the primary. They will skew the primary election in such a way that another John McCain or Bob Dole may win - a compromise candidate the cedes the election to a charismatic Democrat.
This would be a disaster