I would urge a (probably shorter) variant of this:
“We have just experienced one of the worst financial disasters in history. If we think we can prevent a repeat of this by reforming the tax code and repealing a few regulations, we have lost our minds. We need serious, systemic changes, not some talking points from 1982, but that’s all we’re hearing on this stage.
“My supporters are always on my case that I should criticize my opponents more and boast about my record. I prefer to keep the discussion on the level of ideas. But this moment in history is so crucial to our future, and Americans are so uneasy and concerned, that I have no choice. So let me be blunt: I warned of the housing collapse years before it happened, and I have been speaking out against our monetary system — cautioning that it would lead to precisely the kind of collapse we’ve just seen — for decades. My opponents do not even seem interested in figuring out what caused the crisis or trying to make serious repairs to our system. It’s just the same old talking points.
“My fellow Americans, this is serious business. We’re not deciding who’s the most smooth or telegenic. We’re deciding who really understands what’s happening to our economy and knows how to put things right. If you want a president with the credibility and the knowledge to lead our country through this very dangerous moment in history, I am your man.”